Coupling Region Research Articles

Stabilized coupled trajectory mixed quantum-classical algorithm with improved energy conservation: CTMQC-EDI.

Coupled trajectory mixed quantum-classical (CTMQC) dynamics is a rigorous approach to trajectory-based non-adiabatic dynamics, which has recently seen an improvement to energy conservation via the introduction of the CTMQC-E algorithm. Despite this, the method's two key quantities distinguishing it from Ehrenfest dynamics, the modified Born-Oppenheimer momentum and the quantum momentum, require regularization procedures in certain circumstances. Such procedures in the latter can cause instabilities, leading to undesirable effects, such as energy drift and spurious population transfer, which is expected to become increasingly prevalent when the system gets larger as such events would happen more frequently. We propose a further modification to CTMQC-E, which includes a redefinition of the quantum momentum, CTMQC-EDI (double intercept), such that it has no formal divergences. We then show for Tully models I-III and the double arch model that the algorithm has greatly improved total energy conservation and negligible spurious population transfer at all times, in particular in regions of strong non-adiabatic coupling. CTMQC-EDI, therefore, shows promise as a numerically robust non-adiabatic dynamics technique that accounts for decoherence from first principles and that is scalable to large molecular systems and materials.

Autonomous Wireless Power Transfer System with Constant Output Voltage in a Wide Load Range

In this paper, an autonomous wireless power transfer (WPT) system with constant voltage output in a wide load range is presented. Here, combining self-oscillating control and phase-shift control, a new implementation of the autonomous WPT system is proposed. The proposed autonomous WPT system operates using a self-oscillating control method in the strong coupling region, which can automatically maintain the constant output voltage. In the weak coupling region, a phase-shift control method with a fixed frequency and a variable duty cycle is implemented, and a control strategy based on output voltage estimation is proposed to obtain the constant output voltage. In addition, according to the operating frequency characteristic of the proposed autonomous WPT system, a corresponding coupling region judgment method is presented to guarantee the realization of switching between the two control methods. An experimental prototype with a 24 V output voltage is constructed to validate the practicability of the proposed method. The experimental results show the proposed autonomous WPT system can obtain constant output voltage in a wide load range.

Dual Coupled Long-Range Hybrid Surface Plasmon Polariton Waveguide for Sub-Wavelength Confinement.

In this paper, a long-range hybrid waveguide for subwavelength confinement based on double SPP coupling is proposed. The hybrid waveguide consists of a metal-based cylindrical hybrid waveguide and a silver nanowire. There are two coupling regions in the waveguide structure that enhance mode coupling. Strong mode coupling enables the waveguide to exhibit both a small effective mode area (0.01) and an extremely long transmission length (700 μm). The figure of merit (FOM) of the waveguide can be as high as 4000. In addition, the cross-sectional area of the waveguide is only 500 nm × 500 nm, allowing optical operation in the subwavelength range, which helps enhance the miniaturization of optoelectronic devices. The excellent characteristics of the hybrid waveguide make it have potential applications in photoelectric integrated systems.

Catastrogenesis with unstable ALPs as the origin of the NANOGrav 15 yr gravitational wave signal

In post-inflation axion-like particle (ALP) models, a stable domain wall network forms if the model's potential has multiple minima. This system must annihilate before dominating the Universe's energy density, producing ALPs and gravitational waves (a process we dub “catastrogenesis,” or “creation via annihilation”). We examine the possibility that the gravitational wave background recently reported by NANOGrav is due to catastrogenesis. For the case of ALP decay into two photons, we identify the region of ALP mass and coupling, just outside current limits, compatible with the NANOGrav signal.

Renormalization group and spectra of the generalized Pöschl–Teller potential

We study the Pöschl–Teller potential V(x)=α2gssinh−2(αx)+α2gccosh−2(αx), for every value of the dimensionless parameters gs and gc, including the less usual ranges for which the regular singularity at the origin prevents the Hamiltonian from being self-adjoint. We apply a renormalization procedure to obtain a family of well-defined energy eigenfunctions, and study the associated renormalization group (RG) flow. We find an anomalous length scale that appears by dimensional transmutation, and spontaneously breaks the asymptotic conformal symmetry near the singularity, which is also explicitly broken by the dimensionful parameter α in the potential. These two competing ways of breaking conformal symmetry give the RG flow a rich structure, with phenomena such as a possible region of walking coupling, massive phases, and non-trivial limits even when the anomalous dimension is absent. We show that supersymmetry of the potential, when present, is also spontaneously broken, along with asymptotic conformal symmetry. We use the family of eigenfunctions to compute the S-matrix in all regions of parameter space, for any value of anomalous scale, and systematically study the poles of the S-matrix to classify all bound, anti-bound and metastable states, including quasi-normal modes. The anomalous scale, as expected, changes the spectra in non-trivial ways.

Functional to structural plasticity in unilateral sudden sensorineural hearing loss: neuroimaging evidence

A cortical plasticity after long-duration single side deafness (SSD) is advocated with neuroimaging evidence while little is known about the short-duration SSDs. In this case-cohort study, we recruited unilateral sudden sensorineural hearing loss (SSNHL) patients and age-, gender-matched health controls (HC), followed by comprehensive neuroimaging analyses. The primary outcome measures were temporal alterations of varied dynamic functional network connectivity (dFNC) states, neurovascular coupling (NVC) and brain region volume at different stages of SSNHL. The secondary outcome measures were pure-tone audiograms of SSNHL patients before and after treatment. A total of 38 SSNHL patients (21 [55%] male; mean [standard deviation] age, 45.05 [15.83] years) and 44 HC (28 [64%] male; mean [standard deviation] age, 43.55 [12.80] years) were enrolled. SSNHL patients were categorized into subgroups based on the time from disease onset to the initial magnetic resonance imaging scan: early- (n = 16; 1-6 days), intermediate- (n = 9; 7-13 days), and late- stage (n = 13; 14-30 days) groups. We first identified slow state transitions between varied dFNC states at early-stage SSNHL, then revealed the decreased NVC restricted to the auditory cortex at the intermediate- and late-stage SSNHL. Finally, a significantly decreased volume of the left medial superior frontal gyrus (SFGmed) was observed only in the late-stage SSNHL cohort. Furthermore, the volume of the left SFGmed is robustly correlated with both disease duration and patient prognosis. Our study offered neuroimaging evidence for the evolvement from functional to structural brain alterations of SSNHL patients with disease duration less than 1 month, which may explain, from a neuroimaging perspective, why early-stage SSNHL patients have better therapeutic responses and hearing recovery.

A non-volatile optical filter based on a Ge2Sb2Te5-assisted microring with a tunable bandwidth and extinction ratio

A novel non-volatile optical filter with a large bandwidth (BW) and extinction ratio (ER) tunability is first experimentally demonstrated by introducing an all-optical phase change of Ge2Sb2Te5 (GST). The Si-GST hybrid device promises flexible multi-level regulation of essential filter parameters in an ultra-compact footprint of 30 μm × 13 μm. Ultra-low power consumption is realised on account of the saving of external static power that is required in other electric-optic or optic-optic-driven filters. The GST is loaded onto two triple-waveguide directional couplers located at the coupling regions of an add-drop microring resonator. By initiating the GST phase transition with pump optical pulses, the transmitted optical power to the cross port of the triple-waveguide coupler is adjustable, hence influencing the coupling efficiency states of the microring filter. Consequently, a tunable on-off ER from 0.7 dB to 18.2 dB and a tunable BW from 0.6 nm to 3.3 nm are experimentally obtained with the aid of optically manipulating the crystallization degree of GST. Our device potentially enables the realisation of high-density photonic integrated circuits, especially in dense wavelength division multiplexing networks.

A superradiant two-level laser with intrinsic light force generated gain

The implementation of a superradiant laser as an active frequency standard is predicted to provide better short-term stability and robustness to thermal and mechanical fluctuations when compared to standard passive optical clocks. However, despite significant recent progress, the experimental realization of continuous wave superradiant lasing still remains an open challenge as it requires continuous loading, cooling, and pumping of active atoms within an optical resonator. Here we propose a new scenario for creating continuous gain by using optical forces acting on the states of a two-level atom via bichromatic coherent pumping of a cold atomic gas trapped inside a single-mode cavity. Analogous to atomic maser setups, tailored state-dependent forces are used to gather and concentrate excited-state atoms in regions of strong atom-cavity coupling while ground-state atoms are repelled. To facilitate numerical simulations of a sufficiently large atomic ensemble, we rely on a second-order cumulant expansion and describe the atomic motion in a semi-classical point-particle approximation subject to position-dependent light shifts which induce optical gradient forces along the cavity axis. We study minimal conditions on pump laser intensities and detunings required for collective superradiant emission. Balancing Doppler cooling and gain-induced heating we identify a parameter regime of a continuous narrow-band laser operation close to the bare atomic frequency.

Cloud Properties Derived From Airborne Cloud Radar Observations Collected in Three Climatic Regions

AbstractClouds observed by the airborne High‐Performance Instrumented Airborne Platform for Environmental Research (HIAPER) Cloud Radar (HCR) were classified into twelve categories, based on their convective/stratiform nature. Dimensional and convective cloud properties were analyzed in three climatic regions: The subtropical easterlies off the coast of California, the Southern Ocean, and the tropics surrounding Central America. The convective properties of the stratocumulus clouds in the subtropical easterlies are closely related to the degree of boundary layer decoupling. In regions of strong boundary layer coupling, convectivity and updrafts in the clouds are weak and precipitation is light. In regions where the boundary layer is more decoupled, convective properties increase together with cloud top altitudes and cloud depth. Cloud properties of stratocumulus and cumulus clouds over the Southern Ocean show similarities to those observed in the subtropics, but overall they are less convective, indicating a strongly coupled boundary layer. Sea surface temperatures are much lower and the development of clouds is driven by transient synoptic conditions rather than zonal ocean temperature gradients. Clouds observed over the tropical oceans are much more convective in nature. As in the two other regions, they are mostly shallow, but clouds in regions with high sea surface temperatures have high convectivity and reflectivity values and stronger updrafts. Some of them grow to extreme depths (>14 km) and widths (>500 km). They have strong and large updraft regions and are heavily precipitating throughout their life cycle as they transition from the convective to the stratiform stage.

Wide Range Si3N4 Optical Sensor Using Cascaded Mach-Zehnder Interferometer Coupled Ring Resonator

Abstract A cascaded MZI-coupled ring resonator (CMCR) optical sensor based on silicon nitride waveguide is proposed. The sensor is composed of a large size microring and a bus waveguide coupled with the microring for four times. The three-segment bus and the microring waveguide between the four coupling regions form three MZI of the same size, forming a three-stage cascaded MZI. The resonant effect of the cascaded MZI transforms the smooth comb spectrum of the microring into a V-shaped comb spectrum, expands the effective free spectral range of the ring resonator, and realizes the cascaded MZI-coupled microring sensor with a large measurement range. For the cascade MZI-coupled microring with a radius of 100μm, the effective free spectrum range is 53.7nm, which is more than 24 times larger than that of the all-pass microring of the same size. The refractive index sensitivity is 339.49 nm RIU/and the detection limit is 2.95 × 10−5 RIU. these excellent properties prove the feasibility of cascaded MZI-coupled microring structure for large measurement range sensing, and are expected to be used in large refractive index range sensing applications in the future.

Fast Adiabatic Mode Evolution Assisted 2 × 2 Broadband 3 dB Coupler Using Silicon-on-Insulator Fishbone-like Grating Waveguides.

We report a novel 2 × 2 broadband 3 dB coupler based on fast adiabatic mode evolution with a compact footprint and large bandwidth. The working principle of the coupler is based on the rapid adiabatic evolution of local eigenmodes of fishbone-like grating waveguides. Different from a traditional adiabatic coupling method realized by the slow change of the cross-section size of a strip waveguide, a fishbone waveguide allows faster adiabatic transition with proper structure and segment designs. The presented 3 dB coupler achieves a bandwidth range of 168 nm with an imbalance of no greater than ±0.1 dB only for a 9 μm coupling region which significantly improves existing adiabatic broadband couplers.

Coupling-gap free integrated microresonator: Theory and experimental analysis

Microring resonators (MRRs), typically comprising straight and ring waveguides, have played pivotal importance in recent years as far as integrated on-chip systems are concerned. The evanescent coupling in such MRR or solid microdisk resonators is very sensitive to the coupling gap between two waveguides, which affects the resonator’s performance. To overcome the stringent requirement of the gap between two waveguides, we propose a coupling-gap-free, on-chip ellipsoid microresonator. The theoretical framework has been deduced to attain the modal properties of such integrated microresonator geometry, which shows an excellent agreement with the finite difference time domain simulations and experimental results. The absence of a coupling region makes the device uniquely compact and robust, with an insertion loss of ∼5 dB. The resonator’s geometrical dimensions can also be conveniently scaled within certain constraints. The proposed device can be a potential alternative to MRRs and could help in applications such as optical filters, delay lines, on-chip sensing, and many more.

Discretely Tunable (2594, 2629, 2670 nm) GaSb/Si3N4 Hybrid Laser for Multiwavelength Spectroscopy

AbstractA discrete, tunable photonic integrated laser is showcased for multiwavelength spectroscopy of CO2, H2S, and H2O. The laser combines an AlGaInAsSb/GaSb type‐I quantum well‐reflective semiconductor optical amplifier with a Si3N4 photonic integrated circuit (PIC). Operating at room temperature, the laser emits at 2670.42, 2629.12, and 2594.27 nm, with mW‐level average powers. The PIC employs a novel approach for achieving switching between three distinct emission wavelengths by using two cascaded tunable Mach–Zehnder interferometers (MZIs) that are connected to three spiral‐shaped narrow‐band distributed Bragg reflectors (DBRs). Phase tuning the arms of the MZIs allows the laser emission wavelength to be switched between the DBRs, while the DBRs themselves offer fine‐tuning of the emission wavelength. This design enables a simpler tuning mechanism with fewer control variables compared to hybrid PIC‐based lasers using Vernier architectures or a combination of multiple semiconductor amplifiers. Low‐loss and broadband MZIs are achieved by employing two interconnected directional couplers, which utilize asymmetric waveguides in the coupling region to effectively control the phase. Besides achieving state‐of‐the‐art performance for Si3N4‐based integrated lasers at 2.6 µm wavelength region, the demonstrated performance of passive components, including MZIs and spiral DBRs, opens new possibilities for mid‐infrared PIC technology.

On the renormalization of non-polynomial field theories

A class of scalar models with non-polynomial interaction, which naturally admits an analytical resummation of the series of tadpole diagrams is studied in perturbation theory. In particular, we focus on a model containing only one renormalizable coupling that appear as a multiplicative coefficient of the squared field. A renormalization group analysis of the Green functions of the model shows that these are only approximated solutions of the flow equations, with errors proportional to powers of the coupling, therefore smaller in the region of weak coupling. The final output of the perturbative analysis is that the renormalized model is non-interacting with finite mass and vanishing vertices or, in an effective theory limited by an ultraviolet cut-off, the vertices are suppressed by powers of the inverse cut-off. The relation with some non-polynomial interactions derived long ago, as solutions of the linearized functional renormalization group flow equations, is also discussed.

Fano resonance in a microring resonator with a micro-reflective unit

Fano resonance is considered to be a promising approach for integrated sensing. However, achieving and controlling Fano resonance lineshapes on ultra-compact chips remains a challenge. In this article, we propose a theoretic model based on the transfer matrix method (TMM) to quantitatively interpret the impact of a micro-reflective unit (MRU) etched in the straight waveguide of a microring resonator (MRR). Numerical calculations and FDTD simulations indicate that the size and position of the MRU can be used to control the Fano resonance lineshape. Since the MRU is etched in the coupling region, the reflection caused by the MRU will significantly enhance the intensity of the counter-clockwise (CCW) mode in the microring. When applied to a single nanoparticle sensing, clockwise (CW) and CCW modes will couple due to a single nanoparticles or rough cavity walls, resulting in a sharp shift and split of the Fano lineshape. The proposed model for single nanoparticle sensing is described by the scattering matrix, and the calculations show a well matches with FDTD simulations. The results show that the model proposed in this paper provides a new theoretical basis for controlling Fano resonance lineshape and presents a new approach for the integrated sensing of silicon photonic devices with high sensitivity.

Probe of axion-like particles in vector boson scattering at a muon collider

We have examined the sensitivity of the axion-like particles (ALP) couplings to electroweak gauge bosons in the diphoton production at a future muon collider. The collisions at the μ + μ − energies of 3 TeV, 14 TeV, and 100 TeV are addressed. The differential cross sections versus the invariant mass of the final photons and total cross section versus minimal diphoton invariant mass are presented. We have derived the exclusion regions for the ALP-gauge boson coupling. The obtained bounds are much stronger than the current experimental bounds in the ALP mass region 10 GeV to 10 TeV. The partial-wave unitarity constraints on the ALP-gauge boson coupling are estimated. We have shown that the unitarity is not violated in the region of the ALP coupling studied in the present paper.

Metamaterial‐enabled Fully On‐Chip Polarization‐Handling Devices

AbstractPolarization manipulation is essential in photonic integrated circuits and has numerous applications in various fields, such as optical communication, nonlinear optics, and quantum optics. Advances in nanofabrication have enabled the integration of subwavelength‐structured metamaterials on optical waveguides, providing unprecedented optical manipulation capabilities beyond classical waveguide‐based architectures. In this paper, the polarization space is demonstrated to be fully manipulated by a dielectric metamaterial composed of nanoholes and nanoslots. This approach offers competitive performances for key polarization components, including the polarizer, polarization beam splitter, and polarization‐splitter‐rotator, while maintaining ultra‐compact coupling regions of 18×1 µm2, 16×1.1 µm2, and 13×1 µm2 respectively. The devices are designed by manipulating the phase and amplitude of all possible eigenmodes supported in the waveguide, which is inherently scalable and versatile for on‐chip mode and wavefront manipulation. The unique properties of metamaterials provide powerful tools for on‐chip polarization manipulation and offer new possibilities for the development of compact and high‐performance photonic integrated circuits.

A Simple and General Method for Cross-Coupled Bandpass Filters Based on Circular Patch Resonator

In this article, a simple and general method for the design of cross-coupled bandpass filters with compact size is proposed by virtue of the circular patch resonator. Owing to the unique symmetry of the circle, such a circular patch resonator can be freely divided into several circular sector patch resonators along the radii. With this transformation, any two of the divided resonators have a possible coupling region. Specifically, the neighboring resonators have adjacent sides, while the vertices of all resonators are gathered in the center. Given this, the cross couplings can be easily constructed. Moreover, as the circular sector patch resonators with different boundary conditions along two sides have associated resonant properties, both positive and negative couplings can be provided. Consequently, the circular patch resonator should be a good candidate for the design of cross-coupled filters, and the concrete layout of the resultant filter can be determined by the design parameters as extracted from the design specifications. For demonstration, four design examples, including two single-band, one dual-band, and one tri-band bandpass filters, are constructed, fabricated, and measured. All measured results are in good accordance with the synthesized and simulated counterparts, thereby satisfactorily validating the feasibility and universality of the proposed design method.

Autonomous Pulse Frequency Modulation for Wireless Battery Charging With Zero-Voltage Switching

This paper proposes an autonomous pulse frequency modulation (APFM) scheme for wireless battery charging in which the self-excited oscillating (SEO) wireless power transfer (WPT) system can offer output power regulation with reliable zero-voltage switching (ZVS). The key is to utilize the self-excited oscillation feature to adjust the WPT operating frequency autonomously so as to deliver more power in the strong coupling region than the traditional forced-oscillating (FO) WPT system while the transmission efficiency can maintain at a high level. In the weak coupling region, the system becomes equivalent to the FO-WPT system. The pulse frequency modulation enables the system to adjust the output power by changing its duty ratio. Besides, reliable ZVS is achieved by extracting and processing the current signal at the primary side. Both theoretical analysis and experimental verification are provided to support the feasibility of the proposed APFM for SEO-WPT system.

Development of a two-dimensional coupled smoothed particle hydrodynamics model and its application to nonlinear wave simulations

This paper presents a two dimensional two-way coupled model combining Smoothed Particle Hydrodynamics (SPH) based on the Navier–Stokes equations (NSE) and OceanWave3D based on the fully nonlinear potential flow theory (FNPT) in order to efficiently simulate non-linear waves and wave–structure interaction problems. The two models are strongly coupled in space and time domains using a fixed overlapping zone, wherein the information from both solvers is exchanged by relaxation functions. In the SPH model, an open relaxation boundary, which is implemented as open and relaxation zones, is used in the coupling region. Horizontal velocity and free surface elevation in the open and relaxation zones are obtained from OceanWave3D, while vertical velocity and density in the open zones are interpolated from the relaxation region. OceanWave3D requires the free surface elevation and vertical velocity at the free surface from SPH in the coupled region. The coupled model is tested by modelling a regular wave, irregular wave and wave over a submerged bar and an oscillating water column (OWC) device. The results demonstrate that the coupled model can produce satisfactory results with less computational time than the SPH-only model.