Interaction of moiré excitons with cavity photons in two-dimensional semiconductor hetero-bilayers

Moiré materials, composed of two single-layer two-dimensional semiconductors, are important because they are good platforms for studying strongly correlated physics. Among them, moiré materials based on transition metal dichalcogenides(TMDs) have been intensively studied. The hetero-bilayer can support moiré interlayer excitons if there is a small twist angle or small lattice constant difference between the TMDs in the hetero-bilayer and form a type-II band alignment. The coupling of moiré inter...     

A pitch-variation moiré fringes method of temporal phase unwrapping profilometry

A method of pitch-variation moiré fringes is proposed to realize the temporal phase unwrapping for three-dimensional profilometry. On the basis of the principle of moiré pattern,we achieve variable spatial frequencies of fringes in a moiré pattern by rotating two gratings. Furthermore a five-point fitting method is used to automatically compute the central position of side-lobe spectrum of the moiré fringes. Finally,a generalized temporal phase unwrapping algorithm is intro-duced to process the three-dimensional reconstruction. The theoretical analysis and experimental results show the validity of the proposed method.     

Review of phonons in moiré superlattices

Moiré patterns in physics are interference fringes produced when a periodic template is stacked on another similar one with different displacement and twist angles. The phonon in two-dimensional(2D) material affected by moiré patterns in the lattice shows various novel physical phenomena, such as frequency shift, different linewidth, and mediation to the superconductivity. This review gives a brief overview of phonons in 2D moiré superlattice. First, we introduce the theory of the moiréphonon mo...     

Recent progress on fabrication and flat-band physics in 2D transition metal dichalcogenides moiré superlattices

Moiré superlattices are formed when overlaying two materials with a slight mismatch in twist angle or lattice constant. They provide a novel platform for the study of strong electronic correlations and non-trivial band topology, where emergent phenomena such as correlated insulating states, unconventional superconductivity, and quantum anomalous Hall effect are discovered. In this review, we focus on the semiconducting transition metal dichalcogenides(TMDs) based moiré systems that host intrigui...     

Twist-angle two-dimensional superlattices and their application in(opto)electronics

Twist-angle two-dimensional systems,such as twisted bilayer graphene,twisted bilayer transition metal dichalcogenides,twisted bilayer phosphorene and their multilayer van der Waals heterostructures,exhibit novel and tunable properties due to the formation of Moirésuperlattice and modulated Moirébands.The review presents a brief venation on the development of"twistronics"and subsequent applications based on band engineering by twisting.Theoretical predictions followed by experimental realization of magic-angle bilayer graphene ignited the flame of investigation on the new freedom degree,twistangle,to adjust(opto)electrical behaviors.Then,the merging of Dirac cones and the presence of flat bands gave rise to enhanced light-matter interaction and gate-dependent electrical phases,respectively,leading to applications in photodetectors and superconductor electronic devices.At the same time,the increasing amount of theoretical simulation on extended twisted 2D materials like TMDs and BPs called for further experimental verification.Finally,recently discovered properties in twisted bilayer h-BN evidenced h-BN could be an ideal candidate for dielectric and ferroelectric devices.Hence,both the predictions and confirmed properties imply twist-angle two-dimensional superlattice is a group of promising candidates for next-generation(opto)electronics.     

Bonding and thermal stability of implanted hydrogen in silicon

The behavior of implanted hydrogen in Si has been investigated by differential infrared transmittance measurements using multiple-internal-reflection (MIR) plates. Si-H bonding of implanted hydrogen is detected by seven absorption bands between 4.5 and 5.5 μm after implantation with 10¹⁶ H⁺/cm² at ion energies between 70 and 400 keV. The absorption bands are close in frequency to those for SiH stretching modes for silane, and they are produced only by hydrogen implantation. Implantation with deuterium gave absorption bands shifted to lower frequencies in accord with the square root of the reduced mass ratio for Si-H relative to Si-D. The multiplicity of hydrogen-associated bands is apparently a consequence of defects in the implanted layer. A dependence of the hydrogen-associated bands on the disorder is suggested by the annealing loss of five of the initial seven bands, and a growth of the other two, for the same temperatures (100–300°C) as those for annealing out the broad divacancy band at 1.8 μm. A disorder dependence of the Si-H vibrational frequencies is further demonstrated by a regeneration of the bands annealing below 300°C when a hydrogen-implanted MIR plate annealed at 300°C was subsequently bombarded with neon. In addition to the seven resolved bands after H⁺ implantation, five other bands in the same range of frequencies grow in and anneal out between 100 and 700°C. Annealing at 700°C eliminates all SiH bands, and they cannot be regenerated by bombardment with other ions. It is suggested that implanted hydrogen in Si is bonded at defect sites, and that a loss of an SiH band is caused by either a change in charge state of a defect or by the loss of a defect. This work was supported by the United States Atomic Energy Commission     

Transmission spectra of one-dimensional photonic crystals including negative-refractive-index media

We introduce a new model of one-dimensional （1D） photonic crystal composed of alternately arranged RHM and LHM layers with positive and negative refractive indices respectively, for which the transmission spectra of the model are calculated numerically with the transfer matrix method, and the bandgap structure and the polarization properties are analyzed. We found that the introduction of negative refractive index layers （i.e. LHM medium layers） gives rise to some peculiar band-gap structure and polarization properties as follows. Firstly, the forbidden bands are extremely wide and the transmission bands are very sharp without oscillation;and secondly, the change of incident angle has different influences on the forbidden bands of TE and TM modes. For the TM mode, the forbidden band width decreases substantially and finally vanishes, and for the TE mode with central wavelength, the total reflection happens at anv incident anale.     

Preface to Special Topic on Twisted van der Waals Heterostructures

<正>Twisted van der Waals heterostructures are becoming the building blocks for engineering new device structures, in which their electronic, optical and mechanical properties can be tuned by changing the “twist” angle between layers of 2D materials. Such twisted 2D heterostructures offer a unique opportunity to create a new field of “twistronics” by mechanically stacking different 2D van der Waals materials together.     

Research of line-of-sight angle on aero-optic imaging deviation for vehicles flying at 40—60 km

Aero-optical imaging deviation is a kind of optical effect, aiming at a conical aircraft. This paper analyzes the influence of the aircraft on the imaging deviation with the change of altitude and line-of-sight angle. In this paper, the relationships between imaging deviation and altitude as well as line-of-sight angle are analyzed, and the coupling relationship between altitude and line-of-sight angle is studied. We give the imaging deviation results of 5°—75° line-of-sight angle. The analysis shows that when the line-of-sight angle is in the range of 5°—35°, the imaging deviation is more sensitive, while the line-of-sight angle is in the range of 35°—75°, the imaging deviation is relatively flat, and the imaging deviation does not gradually decrease with the increase of line-of-sight angle, but there is a turning point in the middle of 5°—75°. The imaging deviation decreases first and then increases, and the turning point of line-of-sight angle is closely related to height.     

Effect of oblique incidence on bistability of nonlinear microcavity

Based on the nonlinear medium transfer theory, optical bistability of nonlinear microcavity is investigated at oblique incidence. It is found that the critical frequency of incident light inducing bistability phenomenon is related to the polarization and incident angle. The critical frequency increases with the incident angle. Increasing the incident angle can make bistability happen easier for focusing Kerr medium, but will hinder bistability for defocusing Kerr medium. The bistability switch threshold of TE mode is significantly lower than that of TM mode at a large incident angle.     

Birefringent Bragg Gratings in Highly-Nonlinear Photonic Crystal Fiber

Efficient writing of Bragg gratings in 12-ring highly-nonlinear photonie crystal fibers is described. Experimental and numerical investigations are performed to reveal the optimum angle for coupling UV writing light to the core. Furthermore, we show that the formation of a strongly briefringent grating is at a particular angle of orientation.     

Sub-Terahertz Channel Sounder: Review and Future Challenges

Due to the large amount of unused and unexplored spectrum resources, the so-called subTerahertz(sub-THz) frequency bands from 100 to 300 GHz are seen as promising bands for the next generation of wireless communication systems. Channel modeling at sub-THz bands is essential for the design and deployment of future wireless communication systems. Channel measurement is a widely adopted method to obtain channel characteristics and establish mathematical channel models. Channel measurements depend o...     

Reflection and transmission at the surface of a chiral negative refractive medium

Electromagnetic fields at the surface of a chiral negative refraction medium (the chirality parameter is larger than the refractive index) are analyzed theoretically. For obtaining chirality parameter,the normalized reflected and transmitted powers as a function of the incident angle are given for the perpendicular (TE) and parallel (TM) polarized incident wave. Brewster angle and total internal reflection angle are discussed. Due to the negative refraction of one eigen-wave in the chiral medium, the reflection, transmission and Brewster angle characteristics are very different from those in the normal chiral medium.     

Reflection and transmission at the surface of a chiral negafive refractive medium

Electromagnetic fields at the surface of a chiral negative refraction medium （the chirality parameter is larger than the refractive index） are analyzed theoretically. For obtaining chirality parameter,the normalized reflected and transmitted powers as a function of the incident angle are given for the perpendicular （TE） and parallel （TM） polarized incident wave. Brewster angle and total internal reflection angle are discussed. Due to the negative refraction of one eigen-wave in the chiral medium, the reflection, transmission and Brewster angle characteristics are very different from those in the normal chiral medium.     

CORRUGATED CONICAL HORN FOR MULTI-FREQUENCY BAND USE

The theory of corrugated conical horn operating at multi-frequency bands is described,and aprqactical corrugated conical horn is constructed.It can operate at three frequency bands(4,6,11 GHz)atleast.The cross polarization peak level is better than -25 dB at 4,6 GHz frequency bands,and the amplitudepattern at 11 GHz frequency band is also very good.It is shown theoretically and experimentally that thecorrugated conical horn operating at multi-frequency bands is the best condidate for multi-frequency bandfeeds.     

Fluorescence enhancement of single-phase red-blue emit-ting Ba_3MgSi_2O_8:Eu~(2 ),Mn~(2 ) phosphors via Dy~(3 ) addition for plant cultivation

Fluorescence enhancement of red and blue concurrently emitting Ba3MgSi2O8:Eu2 ,Mn2 phosphors for plant cultivation has been investigated by Dy3 addition.The Ba3MgSi2O8:Eu2 ,Mn2 ,Dy3 (BMS-EMD) phosphors have two-color emissions at the wavelength peak values of 437 nm and 620 nm at the excitation of 350 nm.The two emission bands are coincident with the absorption spectrum for photosynthesis of plants.An obvious enhancement effect has been observed upon addition of Dy3 with amount of 0.03 mol%,in which the intensities of both blue and red bands reach a maximum.The origin of red and blue emission bands is analysed.The photochromic parameters of the samples at the nearly UV excitation are tested.This fluoresence enhancement is of great significance for special solid state lighting equipment used in plant cultivation.     

(InSb)m/(HgTe)n短周期超晶格的电子结构

Theelectronicstructureof（InSb）m/（HgTe）nshortperiodsuperlatticesgrownalongthe（001）directionis studiedtheoreticallyusingnorm-conservingpseudo-potentialstogetherwiththelocal-densityapproximationforthe exchange-correlationpotential.Thebandstructuredependsonthevalueofmandn,thenumberofmono-layersand on the ordering of atoms at the InSb/HgTe interface in one unit cell. Our calculation indicates that the superlattice can be a semiconductor having a band gap between the occupied and unoccupied bands, or a metal with no band gap at the Fermi energy. According to the further calculation of total charge density between（InSb）m/（HgTe）nwith different structures, a clearly different behavior happens when the structure changes from a system with a gap and a system without a gap.     

NEDI’2-15GHz Solid-State Power Amplifiers

<正>Applications:Designed primarily for microwave communication system to replace the travelling-wave tube.Used as up-line power amplifier in a small type satellite communication earthetation at C and Ku bands.Features:Employing the power GaAs MESFETs and microstrip circuits with high gain,good lineality,low power consumption and better reliability.     

一个双频带可重构的直接变频接收机射频前端

A dual-band reconfigurable wireless receiver RF front-end is presented, which is based on the directconversion principle and consists of a low noise amplifer （LNA） and a down-converter. By utilizing a compact switchable on-chip symmetrical inductor, the RF front-end could be switched between two operation frequency bands without extra die area cost. This RF front-end has been implemented in the 180 nm CMOS process and the measured results show that the front-end could provide a gain of 25 dB and IIP3 of 6 dBm at 2.2 GHz, and a gain of 18.8 dB and IIP3 of 7.3 dBm at 4.5 GHz. The whole front-end consumes 12 mA current at 1.2 V voltage supply for the LNA and 2.1 mA current at 1.8 V for the mixer, with a die area of 1.2 × 1 mm^2.     

Monolithic Integration DFB Laser Array by Angling Active Stripe and Using Thin-Film Stripe Heater

Multi-wavelength quantum well DFB laser array has been fabricated on an InP substrate by angling the active stripe at an oblique angle to the axis of the grating lines and coating a Pt/Ti thin-film heater to change the laser temperature.Owing to the oblique angle,four single-mode lasing wavelengths around 1.55μm were obtained simultaneously.By changing the working of the thin-film heater,the DFB laser can be tuned continuously beyond a range of 2 2nm with 3.8nm/W of tuning efficiency while maintaining...