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Over the past few decades, on-chip photonic integrated circuits based on silicon photonics (SiPh) platforms have gained widespread attention due to the fact that they offer many advantages, such as high bandwidth, low loss, compact size, low power consumption, and high integration with different photonic devices. The demand for high-speed and high-performance SiPh devices is driven by the significant increase in demand for Internet traffic. In photonic integrated circuits, controlling optical signals to make them circulate in a specific direction is a highly researched area of study. However, achieving a purely passive on-chip optical circulating network on a SiPh platform is very challenging. Therefore, we propose and demonstrate, through simulations, an on-chip optical circulator network on a silicon-on-insulator (SOI) platform. The proposed device can also support mode conversion. The proposed on-chip optical circulating network consists of two kinds of tailor-made multi-mode interferometer (MMI) structures and waveguide crossings. Through the optical power division and mode combination capabilities of the MMI, an optical circulating network supporting high optical isolation and mode conversion is achieved. The proposed optical circulating network has a loss of 1.5 dB at each output port, while maintaining a high isolation of 35 dB in the transmission window from 1530 nm to 1570 nm.

Acoustic manipulation is a set of versatile platforms with excellent manipulation capabilities. In recent years, researchers have increasingly achieved specific manipulations beyond the translation and capture of particles. Here, we focus on the acoustic field momentum mechanism that generates an acoustic radiation force (ARF). A phononic crystal (PC) waveguide is established to amplify the forward momentum of the acoustic beam through the mode conversion of the acoustic field. Based on the conservation of momentum, the object gains reverse momentum. Thus, acoustic pulling can be achieved through the mode conversion of the acoustic field. Furthermore, we analyze the ARFs of two identical objects. It turns out that they can be manipulated separately by opposing forces. Our study provides a new way to achieve stable long-range acoustic pulling, and will explore, beneficially, the interaction between acoustic waves and matter.

In this work, mode conversion and wavefront shaping by integrating a metallic metasurface on top of a planar waveguide are proposed and demonstrated. The metasurface consists of C‐shaped nanoantennas. By controlling the orientation of each nanoantenna, mode conversion and focusing effect for the cross‐polarized electric fields inside the waveguide are achieved. The design and simulation results of 16 scenarios of wideband transverse‐magnetic to transverse‐electric mode converters with the mode purity up to 98%, and on‐chip lenses at the wavelength of 1550 nm are reported. It is worth noting that the dimension of the devices along the propagation direction is only 9.6 µm. This work manifests the potential application of mode division multiplexing systems and on‐chip optical interconnections based on metasurfaces. [ABSTRACT FROM AUTHOR]

Resonant filament-assisted mode conversion (FAMC) scattering of high harmonic fast waves (HHFW) by cylindrical field-aligned density inhomogeneities can efficiently redirect a fraction of the launched HHFW power flux into the parallel direction. Within a simplified analytic approach, this contribution compares the parallel propagation, reflection and dissipation of nearly resonant FAMC modes for three magnetic field line geometries in the scrape-off layer, in the presence of radio-frequency (RF) sheaths at field line extremities and phenomenological wave damping in the plasma volume. When a FAMC mode, excited at the HHFW antenna parallel location and guided along the open magnetic field lines, impinges onto a boundary at normal incidence, we show that it can excite sheath RF oscillations, even toroidally far away from the HHFW launcher. The RF sheaths then dissipate part of the power flux carried by the incident mode, while another part reflects into the FAMC mode with the opposite wave vector parallel to the magnetic field. The reflected FAMC mode in turn propagates and can possibly interact with the sheath at the opposite field line boundary. The two counter-propagating modes then form in the bounded magnetic flux tube a lossy cavity excited by the HHFW scattering. We investigate how the presence of field line boundaries affects the total HHFW power redirected into the filament, and its splitting between sheath and volume losses, as a function of relevant parameters in the model. [ABSTRACT FROM AUTHOR]

A micro structure spiral phase plate (SPP) which is used to generate vortex modes is proposed. The SPP which is designed to be established on a multimode fiber end facet is composed of several groups of fan-shaped glass and air. The effective refractive index changes along the angular direction by changing the ratio of glass to air, and different topological charges are realized by controlling the groove depth. The coupling and propagation processes of Gaussian beams transmitting through the SPP of different topological charges and subsequently into multimode fibers is studied by finite difference time domain (FDTD) simulations. The results show that the Gaussian beam is transformed into several vortex modes after passing through the phase plate, which follows the mode selection rule, that is, the polarization form remains unchanged, the topological charge is equal to that of the SSP, and the root number of the mode is limited to that of the cut-off mode of the fiber. Increase of the absolute value of topological charge leads to the increase of mode size which results in the decrease of the total transmittance. [ABSTRACT FROM AUTHOR]

In a waveguide‐based coupled‐mode system, various mode conversions are achieved by designing mode evolution procedures. However, the differences of refractive indices among modes exceed the capability of conventional tuning mechanism, so most reported mode manipulation devices can only realize fixed mode conversions. This paper introduces the cladding medium switching strategy to the subwavelength grating waveguide‐based coupled‐mode system, and proposes a reconfigurable mode converter on silicon nitride platform. This work systematically analyzes the phase matching conditions on a coupled‐mode system. Results show that for both whole and partial upper‐cladding switchable, it is possible to achieve reconfigurable mode conversions. For whole cladding switchable case, this work demonstrates a double‐state mode converter, which converts the input mode to TE2 and TE1 modes under cladding refractive indices of 1 and 1.7. This work expands it to triple‐state mode conversion with window‐style cladding, which converts the input to TE2, TE1, and TE0 modes under cladding of 1, 1.54, and 1.7. The optical bandwidths are relatively large, and the conversion efficiencies exceed 56% for all cases. The mechanism provides a non‐volatile and energy‐efficient way for tunable mode conversions, which is promising for applications in optical networks, communications, and sensors, etc. [ABSTRACT FROM AUTHOR]

In this work, we propose a mode-conversion-based chirped Bragg grating on thin-film lithium niobate (TFLN). The device is mainly composed of a 4.7-mm long chirped asymmetric Bragg grating and an adiabatic directional coupler (ADC). The mode conversion introduced by the ADC allows the chirped Bragg grating operates in reflection without using an off-chip circulator. The proposed device has experimentally achieved a total time delay of 73.4 ps over an operating bandwidth of 15 nm. This mode-conversion-based chirped Bragg grating shows excellent compatibility with other devices on TFLN, making it suitable in monolithically integrated microwave photonics, sensing, and optical communication systems. [ABSTRACT FROM AUTHOR]

Spherical tokamak plasmas are typically overdense and thus inaccessible toexternally-injected microwaves in the electron cyclotron range. Theelectrostatic electron Bernstein wave (EBW), however, provides a method toaccess the plasma core for heating and diagnostic purposes. Understanding thedetails of the coupling process to electromagnetic waves is thus important bothfor the interpretation of microwave diagnostic data and for assessing thefeasibility of EBW heating and current drive. While the coupling is reasonablywell-understood in the linear regime, nonlinear physics arising from high inputpower has not been previously quantified. To tackle this problem, we haveperformed one- and two-dimensional fully kinetic particle-in-cell simulationsof the two possible coupling mechanisms, namely X-B and O-X-B mode conversion.We find that the ion dynamics has a profound effect on the field structure inthe nonlinear regime, as high amplitude short-scale oscillations of thelongitudinal electric field are excited in the region below the high-densitycut-off prior to the arrival of the EBW. We identify this effect as theinstability of the X wave with respect to resonant scattering into an EBW and alower-hybrid wave. We calculate the instability rate analytically and find thisbasic theory to be in reasonable agreement with our simulation results.

One barrier, preventing the wide applications of elastic metamaterials (EMMs), is their limited ability to attenuate waves at low frequencies. Rainbow metamaterials (RMs), characterized by spatially varying structural parameters, can exhibit outstanding performance, boosting wider wave attenuation frequency ranges (stopbands) at lower frequencies compared to their counterparts of finite EMMs. However, attributed to the intricate topologies and constitutive relationships in 3D RMs, effectively configuring them to achieve enhanced wave-suspending capability is challenging. In most existing design approaches, frequency response analysis (FRA) method is frequently employed to iteratively calculate reliable stopband characteristics, leading to a significant computational burden. Herein, to address these challenges, a novel mode conversion approach is developed, underpinned by a recently proposed modal-based evaluation method (MEM) to estimate stopband characteristics, and a novel layer-based energy manipulation strategy to redirect energy, originating in excitation place, away from the output. The proposed approach is demonstrated to be effective for 3D RM design, through guiding the adjustment of geometrical parameters (GPs) of unit cells in each layer on 3D RMs. Moreover, the structure robustness is tested through experiments, facilitating the applications of 3D metamaterials. • Proposed a modal analysis-aided approach for 3D metastructure design. • Able to Estimate starting and cut-off frequencies via dominant eigenmode superposition. • Tuned geometrical parameters based on mode classification results. • Tuning geometrical parameters lowered starting frequency and enlarged normalized bandwidth simultaneously. [ABSTRACT FROM AUTHOR]

In this article, a 90°-bent differential transmission line using the asymmetric periodic structure filter is proposed. The asymmetry of the periodic structure filter is used to reduce the differential-to-common mode conversion while the frequency response of the periodic structure filter is used to reflect the common-mode noise. As compared with the conventional 90°-bent differential transmission line, the differential-to-common mode conversion is greatly reduced from −3.04 to −20.42 dB while the time-domain differential-to-common mode transmission is greatly reduced from 0.094 to 0.006 V. Besides, the common-mode reflection coefficient is largely increased from −13.72 to −0.94 dB while the time-domain common-mode reflection is largely increased from 0.017 to 0.068 V. Furthermore, the performance of the eye diagram is upgraded, meaning that the signal integrity is improved. [ABSTRACT FROM AUTHOR]

In this letter, we propose a method to realize rectangular waveguide mode to spoof surface plasmon polaritons (SSPP) mode conversion using phase gradient metasurface (PGM). By applying a PGM with designed wavevector to the narrow wall of the rectangular waveguide, propagation mode and direction of the guided waves can be conversed and controlled due to wavevector matching. Such system can provide an excellent transition by matching the momentum of the rectangular waveguide mode and the SSPP mode. A smooth bridge between the rectangular waveguide system and the SSPP waveguiding system can be realized with potential advantages in conformal design, super-resolution imaging or signal manipulation. Simulated and experimental results, agreeing well with each other, validated the effectiveness of rectangular waveguide mode to SSPP mode conversion using PGM from 6.96-7.55 GHz. Furthermore, a dual channel rectangular waveguide to SSPP splitter is proposed and validated with applications for dual-channel power dividing and signal transmission, achieving an efficiency of 72.4%. [ABSTRACT FROM AUTHOR]

We have studied the transmission properties of odd/even one-way modes and their reversible conversion in a double-channel waveguide consisting of two magneto-optical photonic crystals (MOPCs) sandwiched with Al2O3 PC. There exist two pairs of even and odd modes, i.e., M1(even)/M2(odd) or M3(odd)/M4(even) modes, for the double-channel waveguides with one- or two-stranded coupling layer of Al2O3 rods, respectively. Among them, the M1, M2, and M3 modes are caused by the weak coupling strength of two sub-waveguides, while the M4 mode results from the strong coupling effect and supports dispersionless slow-light propagation. Furthermore, we realize the reversible conversion between odd and even modes (i.e., between M1 and M2 modes, or M3 and M4 modes) in the one- or two-stranded structure, respectively, by adjusting the length and position of the perfect electric conductor (PEC) defect properly to cause the desired significant phase delay along the upper and lower equivalent transmission paths. Additionally, we find that the robustness of the M1 even mode is poor because of extra excitations of counter-propagation modes near the right Brillouin boundary, while the other three modes have extremely strong robustness against PEC defects and their one-way transmittances are nearly 100%. These results hold promise for many fields, such as slow-light modulation and the design of topological devices. [ABSTRACT FROM AUTHOR]

Mode-converting metasurfaces are passive, lossless devices that can be designed to transform a set of incident modes to a desired set of transmitted modes. In this paper, mode-converting metasurfaces are utilized to synthesize arbitrary, azimuthally-invariant TM apertures. The methods presented in this work can be used to design antennas that can meet specific near-field and far-field criteria unlike most metasurfaces which solely manipulate the far field. The proposed antennas consist of a coaxially-excited, radial cavity topped by the mode-converting metasurface. The main role of the mode-converting metasurface is to establish the desired aperture by converting the modal distribution of the excitation to that of desired aperture. Its secondary role is to impedance match the coaxial feed to the radial cavity. Using modal network theory, an optimization-based design procedure is developed to synthesize the proposed metasurface antennas. The admittance profiles of the electric sheets that comprise the metasurface are optimized to establish the desired aperture profile. To illustrate the design procedure, a radial Gaussian beam antenna is synthesized at 10 GHz and its performance is verified using a full wave electromagnetic solver. The proposed antenna has a height and weight advantage over Gaussian beam horn antennas.

Shear Horizontal (SH) guided waves have been extensively used to estimate and detect defects in structures like plates and pipes. Depending on the frequency and plate thickness, more than one guided-wave mode propagates, which renders signal interpretation complicated due to mode mixing and complex behavior of each individual mode interacting with defects. This paper investigates the use of machine learning models to analyse the two lowest order SH guided modes, for quantitative size estimation and detection of corrosion-like defects in aluminium plates. The main contribution of the present work is to show that mode separation through machine learning improves the effectiveness of predictive models. Numerical simulations have been performed to generate time series for creating the estimators, while experimental data have been used to validate them. We show that a full mode separation scheme decreased the error rate of the final model by 30% and 67% in defect size estimation and detection respectively.

An optical switch based on silicon-on-insulator (SOI) technology is proposed that works in the C-band and switches by amorphous (Am) to crystalline (Cr) and Cr-to-Am phase transitions. The optical switch integrates the functions of polarization beam splitting and mode conversion, and consists of two asymmetric directional couplers (ADCs). The TM0 mode is converted to the TM1 mode through an asymmetric coupler to achieve the polarization splitting of the TM0 mode and TE0 mode. The output of the TE0 mode is then controlled by Ge2Sb2Se4Te1 (GSST). When the TE0 mode is input and the wavelength is 1550 nm, the insertion loss (IL) is lower than 0.62 dB and the crosstalk (CT) is lower than −9.88 dB for a directional coupler loaded with GSST that realizes the optical switch function in both amorphous and crystalline GSST. The extinction ratio (ER) of the two waveguides of the directional coupler is lower than −11.40 dB, simultaneously. When the TM0 mode is input and the wavelength is 1550 nm, the IL is lower than 0.62 dB for a directional coupler loaded without GSST. [ABSTRACT FROM AUTHOR]

A circularly polarized high-power antenna with higher-order mode excitation (TM01) is presented in this paper. The proposed structure consists of metal plates placed on the conical horn antenna's aperture for achieving TM01 to circular polarized TE11 mode conversion at the output. The structure is simulated on CST Microwave Studio. The designed antenna exhibits high gain and a directive radiation pattern. The axial ratio of the proposed structure is below 3 dB. The simulated and measured reflection coefficient for TM01 mode excitation is below −10 dB over a frequency range of 2.95–3.13 GHz. The structure is purely metallic, and the calculated high-power microwave (HPM) capability is up to the MW level. The proposed antenna is helpful for portable HPM systems. [ABSTRACT FROM AUTHOR]

Highly oversized mode converters are the critical devices for high power millimeter-wave transmission systems, characterizing high power capacity and low loss. In order to improve the conversion efficiency from TE01 to TE11 mode, the mode coupling mechanism of oversized elliptical waveguides is explored, and an optimal ellipticity interval to obtain the high conversion efficiency is deduced by analyzing the mode coupling capacity. Considering that ellipticity can affect the power capacity, breakdown thresholds of different operating modes in elliptical waveguides are studied. Based on the analyses, a synthesis method to design the elliptical mode converter integrating the mode conversion efficiency and the power capacity is proposed. A highly oversized mode converter working in $W$ -band is designed, and the simulation results demonstrate that the mode converter achieves the high conversion efficiency over 95% in a relative bandwidth of 19.6%. In order to validate the design, a prototype of the mode converter is fabricated, and the high purity of outputted TE11 mode is verified by the measurement. The oversized mode converter designed by the proposed synthesis method features high efficiency, broad bandwidth, and high power capacity, enabling its full utilization of the potential of gyrotron traveling-wave tubes (gyro-TWTs). [ABSTRACT FROM AUTHOR]

Abstract The mode conversion process responsible for radio wave generation has been studied for several decades; however, the properties of the condition required for an efficient conversion process are still unknown. The aim of this study is to determine the value of plasma frequency required for an efficient mode conversion process from slow Z-mode to left-hand ordinary (LO)-mode waves in the matching cases, where the two branches of the dispersion relation of the two modes are perfectly connected. We derive the dispersion relations for electromagnetic wave propagation in an inhomogeneous plasma considering Snell’s law and investigated them in detail. We quantify the minimum variation of plasma frequency required for the efficient mode conversion process, which we call “the plasma frequency demand.” We show that the condition required for the efficient mode conversion can be satisfied by waves propagating first toward the high-density region and then returning toward the low-density region before reaching the region where the wave frequency matches the cutoff frequency; therefore, a large inhomogeneity is not always required. We show that the angle between the background magnetic field and the density gradient has a significant effect on the plasma frequency demand.

An ultrasonic wave mode-based method for density measurement in highly foamed batters was developed. Therefore, a non-contact ultrasonic sensor system was designed to generate signals for batch-wise processes. An ultrasonic sensor, containing a piezoelectric ceramic at the fundamental longitudinal frequency of 2 MHz, was used to take impedance measurements in pulse-echo mode. The ultrasonic signals were processed and analysed wave-mode wise, using a feature-driven approach. The measurements were carried out for different mixing times within a container, with the attached ultrasonic sensor. Within the biscuit batter, the change to the ultrasonic signals caused by density changes during the batter-mixing process was monitored (R2 = 0.96). The density range detected by the sensor ranges between 500 g/L and 1000 g/L. The ultrasonic sensor system developed also shows a reasonable level of accuracy for the measurements of biscuit batter variations (R2 > 0.94). The main benefit of this novel technique, which comprises multiple wave modes for signal features and combines these features with the relevant process parameters, leads to a more robust system as regards to multiple interference factors.

The Kelvin–Helmholtz (KH) instability of magnetohydrodynamic surface waves at the low latitude boundary layer is examined using both an eigenfrequency analysis and a time-dependent wave simulation. The analysis includes the effects of sheared flow and Alfvén velocity gradient. When the magnetosheath flows are perpendicular to the ambient magnetic field direction, unstable KH waves that propagate obliquely to the sheared flow direction occur at the sheared flow surface when the Alfvén Mach number is higher than an instability threshold. Including a shear transition layer between the magnetosphere and magnetosheath leads to secondary KH waves (driven by the sheared flow) that are coupled to the resonant surface Alfvén wave. There are remarkable differences between the primary and the secondary KH waves, including wave frequency, the growth rate, and the ratio between the transverse and compressional components. The secondary KH wave energy is concentrated near the shear Alfvén wave frequency at the magnetosheath with a lower frequency than the primary KH waves. Although the growth rate of the secondary KH waves is lower than the primary KH waves, the threshold condition is lower, so it is expected that these types of waves will dominate at a lower Mach number. Because the transverse component of the secondary KH waves is stronger than that of the primary KH waves, more efficient wave energy transfer from the boundary layer to the inner magnetosphere is also predicted.

Perkins et al (2012 Phys. Rev. Lett. 109 045001) reported unexpected power losses during high harmonic fast wave (HHFW) heating and current drive in the National Spherical Torus Experiment (NSTX). Recently, Tierens et al (2020 Phys. Plasmas 27 010702) proposed that these losses may be attributable to surface waves on field-aligned plasma filaments, which carry power along the filaments, to be lost at the endpoints where the filaments intersect the limiters. In this work, we show that there is indeed a resonant loss mechanism associated with the excitation of these surface waves, and derive an analytic expression for the power lost to surface wave modes at each filament. [ABSTRACT FROM AUTHOR]

This study experimentally investigates the efficacy of TE11 mode microwaves in detecting bend-region cracks. Three types of bends with different dimensions were deployed in a 3 m piping system and then tested, with an axial or circumferential slit machined at different angular positions to simulate a crack. The TE11 mode microwaves were excited using self-designed TE11 mode microwave probes and utilised for crack detection. The experimental results show clear reflection peaks at the bend position, demonstrating the feasibility of applying TE11 mode microwaves in the detection of bend-region cracks. Furthermore, the peak location of reflection is in accordance with the angular position of the slit. The findings also indicate that the peak amplitude of reflection is affected by the factors of mode conversion of microwaves at a bend. In addition, the experimental results also manifest an excellent signal-to-noise ratio to both two types of slits, suggesting that the microwave NDT is a powerful tool for bend-region inspection. [ABSTRACT FROM AUTHOR]

Quantitative guided wave thickness mapping in plate-like structures and pipelines is of significant importance for the petrochemical industry to accurately estimate the minimum remaining wall thickness in the presence of corrosion, as guided waves can inspect a large area without needing direct access. Although a number of inverse algorithms have been studied and implemented in guided wave reconstruction, a primary assumption is widely used: the three-dimensional guided wave inversion of thickness is simplified as a two-dimensional acoustic wave inversion of velocity, with the dispersive nature of the waves linking thickness to velocity. This assumption considerably simplifies the inversion procedure; however, it makes it impossible to account for mode conversion. In reality, mode conversion is quite common in guided wave scattering with asymmetric wall loss, and compared with nonconverted guided wavemodes, converted modesmay provide greater access to valuable information about the thickness variation, which, if exploited, could lead to improved performance. Geometrical full waveform inversion (GFWI) is an ideal tool for this, since it can account for mode conversion. In this paper, quantitative thickness reconstruction based on GFWI is developed in a plate cross-section and applied to study the performance of thickness reconstruction using mode conversion. [ABSTRACT FROM AUTHOR]

In this report, mode conversion based on the lateral misalignment between two similar multi-ring core fibers (M-RCFs) is proposed. The conversion was achieved by varying the lateral height (y) and the distance (x) that separates the two M-RCFs. Based on the achieved coupled power of 94%, this technique may find application as a conversion device during multiplexing in mode-division multiplexed systems (MDM). [ABSTRACT FROM AUTHOR]

Asymmetric transmission in which wave energy propagates only in one direction attracts significant attention in various fields because of its rich physics and potential applications. In this work, we propose an elastic mode-converting metamaterial, which allows a full-power mode-converting transmission from longitudinal waves to transverse waves in the forward direction, while completely restricts the L wave transmission in the inverse direction. The metamaterial is designed by simply cutting two arrays of periodic silts on a matrix by exploring a straight design methodology, and thus very friendly for fabrication and application. Eigen-frequency analysis shows that the bilayer metamaterial exhibits two modes with significantly close natural frequencies around the working frequency, one for full-power mode-converting transmission, and the other for asymmetric transmission. Ultrasonic experiments are carried out to validate the proposed design. Our work offers a simple and efficient way for the realization of a complete one-way mode-converting transmission, and could be critically useful in designing diode-like meta-devices for novel wave manipulations.

Compared with thrombus dissolution using only thrombolytic agents, an advanced therapy of direct stirring of the blood clot can yield shorter recanalization time and higher recanalization velocity. Our previous research presented the design of a novel micro-stirrer, which can convert longitudinal vibration into transverse vibration and eventually generate opposite transverse vibration at the end-effort, like a scissor, for efficient blood clot stirring and thrombus dissolution acceleration. Transverse vibration is the most effective movement to dissolve thrombi. However, the small size of blood vessels has strict limits, which will greatly affect the output transverse vibration. Therefore, to improve the output performance of the micro-stirrer in curved and narrow vascular spaces, the analysis and structure optimization of the micro-stirrer is expected to increase the vibration mode conversion efficiency from longitudinal to transverse mode. The design concept and theoretical analysis of the micro-stirrer are presented in detail. Aiming to obtain the optimal structure parameters of the micro-stirrer, the mathematical model is established and analyzed. Next, a series of finite element models involving important structure parameters are designed and investigated. Finally, the optimal structure parameters are obtained, and the stirring effect in a blood vessel is verified by simulation and experiment.

Ion cyclotron range of frequency waves in hot plasmas exhibit spatial dispersion effects and the wave equation takes the integro-differential form. Under the local plasma model assumption, the wave equation can be simplified to the differential form and adapts to the numerical scheme of the finite element method (FEM). Even though direct absorption of fast waves by ions and electrons can be described well by the local plasma model, linear mode conversion associated with non-local effects is absent. To deal with this issue, an alternative method is put forward in this paper where quasi-electrostatic fluid waves based on the multi-fluid warm plasma model are employed to take the place of ion Bernstein waves in mode conversion. On this basis, an interative fluid-kinetics (INTFLUK) code based on the FEM is developed for full-wave simulation in hot plasmas. Derivation of the wave equations as well as benchmarking of the INTFLUK code against other wave simulation codes are carried out. In both one- and two-dimensional cases, the validity of the INTFLUK code was verified by comparison of the wave field distributions and power deposition. As a useful illustration of the INTFLUK code including the scrape-off layer and a realistic antenna, the influence of the poloidal antenna phasing difference on ion cyclotron resonance heating is analyzed. Finally, it should be noted that the method in this paper has the potential to be extended to the three-dimensional case, which will be considered in the near future.

The technique of sound insulation has a wide range of potential applications in environment noise control and architectural acoustics. The rapid development of acoustic artificial materials has provided alternative solutions to design sound insulation structures. However, the realization of single-layer planar structures with bidirectional acoustic insulation (BAI) and unidirectional acoustic insulation (UAI) still poses a challenge. Here, we report the theoretical and experimental realization of two types of single-layer phased array lenses which presents the characteristics of broadband BAI and multi-channel UAI. Both types of lenses consist of 12 mode-conversion phased units which are composed of two types of unit cells (I and II) with an opposite phase and a step waveguide. Based on the phase regulation, the designed phased unit can realize the mode conversion between the zero-order and first-order waves and asymmetric sound manipulation, which enables multi-functional sound insulations. Based on the desired theoretical phase profiles, two types of lenses with BAI and UAI are realized for the incidence of the zero-order wave, and their fractional bandwidths can reach about 0.28 and 0.37, respectively. More interestingly, the UAI effect can be reversed for the incidence of the first-order wave. The proposed lenses based on the mode-conversion phased units have the advantages of single-layer planar structure, multi-functional sound insulation, and broad bandwidth, which have wide application prospect.

Graphene-based reinforcements can enhance mechanical performances of composite structures by altering the distributions of graphene platelets (GPLs), which determines wave propagation characteristics. Dispersion behaviors of elastic waves in the nanocomposite annular plates are investigated in this work. Utilizing the modified micromechanical model and the rule of mixtures, four types of distribution patterns are considered to evaluate the effective material properties of the nanocomposites. Elastodynamic equations of wave motion are expressed and parameterized in the semi-analytical formulation based on Reddy's higher-order shear deformation theory and the isogeometric analysis. Dispersion characteristics of the in-plane and out-of-plane wave modes are studied in detail. The cutoff frequencies are discussed in order to confirm the accuracy of the results. Besides, parametric studies are conducted to analyze the influences of distribution, weight fraction and size parameters of GPLs on phase-velocity and group-velocity curves of waves. The results indicate that the concentration of GPLs on the boundaries of composite plates can improve the propagation characteristics of wave modes. In the case of FG-V, there exists the interesting phenomenon of mode conversion. It is concluded that dispersion characteristics of elastic waves in nanocomposite annular plates can be flexibly modulated by changing significant parameters of the reinforcement GPLs. [ABSTRACT FROM AUTHOR]

A tunable bandwidth add-drop filter in ideal quasi-critical coupling (QCC) state was analyzed in theory in detail and demonstrated in experiment, with two vector modes HE $^{\rm X}_{11}$ and HE $^{\rm Y}_{11}$ coupled single whispering gallery mode (WGM) as its basic configuration. In the experiment, the bandwidth tuning range at the Drop port was from 54.0 MHz to 775.8 MHz with the conversion efficiency maintained above 95%, and bandwidth tuning range at the Through port was from 6.6 MHz to 720.6 MHz with the insertion loss fluctuation less than 5%. The demonstrated filter gains advantages of stable efficiency, narrow band, and broad bandwidth tuning range, which will be helpful for its application in microwave photonics, narrow linewidth lasers and nonlinear optics. [ABSTRACT FROM AUTHOR]

• Mode conversion of incident S 0 Lamb wave mode to A 0 mode at a crack-like defect. • Good agreement between FE and experimental results to validate simulation prediction. • Highest mode conversion ratio obtained at 3/4-thickness depth defect. • Mode-converted, scattered A 0 mode amplitude increases linearly with defect length. Guided ultrasonic waves can be employed for efficient structural health monitoring (SHM) and non-destructive evaluation (NDE), as they can propagate long distances along thin structures. The scattering (S 0 mode) and mode conversion of low frequency guided waves (S 0 to A 0 and SH 0 wave modes) at part-thickness crack-like defects was studied to quantify the defect detection sensitivity. Three-dimensional (3D) Finite Element (FE) modelling was used to predict the mode conversion and scattering of the fundamental guided wave modes. Experimentally, the S 0 mode was excited by a piezoelectric (PZT) transducer in an aluminum plate. A laser vibrometer was used to measure the out-of-plane displacement to characterize the mode-converted A 0 mode, employing baseline subtraction to achieve mode and pulse separation. Good agreement between FE model predictions and experimental results was obtained for perpendicular incidence of the S 0 mode. The influence of defect depth and length on the scattering and mode conversion was studied and the sensitivity for part-thickness defects was quantified. The maximum mode conversion (S 0 -A 0 mode) occurred for ¾ defect depth and the amplitude of the mode-converted A 0 and scattered S 0 modes mostly increased linearly as the defect length increased with an almost constant A 0 /S 0 mode scattered amplitude ratio. Similar forward and backward scattering amplitude was found for the mode converted A 0 mode. The mode conversion of the S 0 to SH 0 mode has the highest sensitivity for short defects, but the SH 0 mode amplitude only increased slightly for longer defects. Employing the information contained in the mode-converted, scattered guided ultrasonic wave modes could improve the detection sensitivity and localization accuracy of SHM algorithms. [ABSTRACT FROM AUTHOR]

In this paper, a 1×4 ultra-compact wavelength division multiplexing cascaded device(DMC) with an arbitrary splitting ratio based on adjoint topology optimization reverse design is proposed, which is approximately two orders of magnitude smaller than that of conventional waveguide devices. It can simultaneously perform wavelength demultiplexing, mode conversion, and arbitrary ratio power splitting. The DMC separates 1310 nm and 1550 nm wavelengths, converts the input light from fundamental transverse mode (TE0) to first-order transverse mode (TE1) and second-order transverse modes (TE2), and performs arbitrarily proportional power splitting of the converted higher-order light source. • An ultra-compact 1×4 DMC with an arbitrary splitting ratio based on adjoint method reverse design is proposed in this paper. It is located on a 220 nm thick SOI platform and simultaneously achieves wavelength demultiplexing, arbitrary proportional power division, and mode conversion. • Meanwhile, the footprint of the WDM and the arbitrary ratio splitter remains fixed, but the footprint of the bent waveguide is enlarged to 2.4 µm×2.4 µm. The widths of the input and output waveguides of the splitter are expanded to 0.9 µm. FDTD simulation results indicate that the device converts the TE0 mode to the TE1 mode. • In addition, the footprint of the WDM stays similar, with the increased footprint of the bent waveguide and arbitrary ratio splitter being 2.4 µm×3.6 µm and 4 µm×4.8 µm, respectively. Furthermore, the output waveguide width of the arbitrary ratio splitter is raised to 1.4 µm. FDTD simulation results indicate that the device will convert the TE0 mode to the TE2 mode. [ABSTRACT FROM AUTHOR]

In this work, we propose a mode-conversion-based chirped Bragg grating on thin-film lithium niobate (TFLN). The device is mainly composed of a 4.7-mm long chirped asymmetric Bragg grating and an adiabatic directional coupler (ADC). The mode conversion introduced by the ADC allows the chirped Bragg grating operates in reflection without using an off-chip circulator. The proposed device has experimentally achieved a total time delay of 73.4 ps over an operating bandwidth of 15 nm. This mode-conversion-based chirped Bragg grating shows excellent compatibility with other devices on TFLN, making it suitable in monolithically integrated microwave photonics, sensing, and optical communication systems.

An ultra-compact multimode wavelength demultiplexer (MWD) with a footprint of 3.6 × 2.4 μm2 was designed. Its size is approximately two orders of magnitude smaller than the size of the traditional waveguide-based device. Moreover, the designed demultiplexer is multifunctional, and can realize wavelength demultiplexing and mode conversion at the same time. This MWD splits light at the wavelengths of 1450 nm and 1550 nm and simultaneously converts the input light from the fundamental transverse electric (TE0) mode to the first-order transverse electric (TE1) mode. The direct binary search (DBS) algorithm was employed to simulate the design. The results show that the insertion loss of the demultiplexer is −1.26 dB and −0.82 dB for the upper channel (wavelength 1450 nm) and lower channel (wavelength 1550 nm), while the crosstalk values are maintained as low as −18.10 dB and −23.35 dB, respectively. Additionally, a similar structure can be expanded to several modes. Based on these advantages, this multifunctional photonics device is expected to be used extensively in advanced photonic integration circuits.