Transverse Mode Research Articles

All‐metal wide‐angle and polarization‐independent microwave metamaterial absorber

AbstractAn innovative all‐metal self‐support microwave metamaterial absorber (MMA) based on a continuous complementary split ring resonator (CSRR) array frequency selective surface (FSS) is constructed. The CSRR‐based FSS has a selected frequency of 23 GHz and is proved to be polarization insensitive. And the all‐metal MMA has the same response frequency as the FSS, showing convenience in the geometrical scaling process. Additionally, in both transverse electric and transverse magnetic modes, the all‐metal MMA shows stable response at oblique incidences with an incident angle as large as 50°. Along with lightweight, easy fabrication and high cost‐performance ratio, the new proposed all‐metal FSS‐based MMA has good potential to serve in many practical applications.

Intrinsic resonance in gyrotron using non-resonant RF structure

Gyromonotrons are typically believed to rely on the convective interaction between the co-propagating beam and wave, with the extended energy-exchanging process stemming from the external feedback. However, numerous studies focusing on both transverse electric (TE) mode and transverse magnetic (TM) mode gyrotrons have consistently shown that beam–wave interactions in weak-feedback systems or even in uniform tubes without any structural feedback can yield a theoretical beam efficiency of more than 30% with major forward-wave output during near-cutoff operation, which is the typical operating condition for gyromonotrons. These intriguing findings raise questions about the actual feedback mechanism of gyromonotrons. In this article, comparative studies on the linear and nonlinear behaviors of uniform-tube gyrotron are investigated. The forward and backward waves are observed to co-generate and exhibit similar characteristics of ultra-slow group velocity under near-cutoff operation. This situation allows the as-generated forward wave to modulate the fresh beam, establishing a new backward-wave-like internal feedback loop. Additionally, the quasi-degenerate nature of the bi-directional propagating waves ensures their intrinsic in-phase relationship. The consequent constructive interference enables the uniform tube to function as a high-Q resonator. These findings are found to be independent of the choices of TE or TM modes, providing valuable insights into the underlying interaction mechanism of gyrotron devices.

Voltage-tunable graphene-InP schottky photodetector with enhanced responsivity using plasmonic waveguide integration

In this work, we propose and theoretically investigate a novel side-illuminated graphene Schottky photodetector (SIGS-PD) integrated on an InP waveguide platform suitable for the telecommunication wavelength of 1.55 μm. Bilayer graphene is positioned to absorb the transverse magnetic (TM) mode, with an InP substrate forming a Schottky junction to enable electrical connectivity and carrier separation. Through electrostatic gating, the graphene Fermi level is actively tuned to reach an epsilon-near-zero condition of 0.51 eV, transitioning the optical properties from dielectric to metallic. This supports reconfigurable plasmonic modes confined within the subwavelength graphene layer, interacting strongly with the TM optical mode. Responsivity of TM mode is enhanced 10 × TE mode reaching 1.24 A W−1 at the epsilon-near-zero point for the wavelength of 1.55 μm due to discontinuity and localization of the perpendicular electric field. The maximum responsivity is achieved at reverse bias of 4.5 V for device lengths under 4 μm. Dark current is suppressed to 10−15 A by the rectifying Schottky junction. An internal specific detectivity of 9.6 × 1012 Jones is predicted along with >25 GHz bandwidth, exploiting combined benefits of plasmonic enhancement and electrical transport control in the hybrid graphene-InP platform. The voltage-tunability of the graphene optical properties provides a pathway to dynamically optimize device performance. This work demonstrates a route towards high-responsivity and high-speed graphene photodetectors seamlessly integrated with photonic integrated circuits.

Precise evaluation of the material constants of [011]-poled mangan-doped 0.32Pb(In1/2Nb1/2)O3-0.39Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 single crystals

Recently, there has been a surge of interest in [011]-poled Mn: PIN-PMN-PT piezoelectric single crystals for high-power transducers. These crystals boast impressive electromechanical coupling coefficients, piezoelectric constants in the transverse mode, and excellent heat resistance due to their high mechanical quality factor. To effectively design transducers using these crystals, understanding their material constants is crucial. Our study focused on determining these constants by employing the resonance method. We created eleven different resonators, analyzed their impedance spectra, and derived seventeen elastic compliance, piezoelectric, and dielectric constants. The precision of the obtained material constants was enhanced by minimizing the difference between the impedance spectra found through finite element analyses and actual measurements of each resonator. The accuracy of these derived constants was validated by comparing the impedance spectra obtained from analysis with those measured experimentally. This novel approach demonstrated a capability to derive more precise material constants than prior studies. These refined material constants hold the potential to enable more precise and effective design of acoustic transducers constructed from the single crystals.

Design of miniaturized 2.5D frequency selective surface for X‐ and Ku‐band applications

AbstractThis paper presents the design of 2.5D frequency selective surface (FSS) for X and Ku band applications. Proposed FSS's unit cell is constructed with two independent slitted rings on both side of the FR4 substrate and is connected with metallic vias. The FSS offers a wide stop band performance from 6.26 to 18 GHz, with a fractional bandwidth of 96.7% measured at S21 < −10 dB and has a low insertion loss (IL) of 0.018 dB. The footprint of the FSS is only about 0.11 with the shielding effectiveness of 83.365 dB, and the transverse electric and transverse magnetic mode performances are stable up to 70 degrees. Prototype FSS is fabricated and measured for its performance validation. The performance validation is carried out using applied wave research and the equivalent circuit model tools.

Use of periodic 2D pillar array for performance enhancement of AlN-based SMR BAW resonators

This paper discusses the applicability of a two-dimensional (2D) periodic pillar array as the first layer of an acoustic mirror for AlN-based solidly mounted resonators of bulk acoustic waves. It is based on the idea that the periodic pillar array behaves like a uniform layer when the period is much smaller than the wavelength and its behavior is given by the ensemble average of pillar materials. The simulation shows that the effective electromechanical coupling factor can be enhanced close to that of AlN-based film bulk acoustic resonators when the slot ratio is large. It is also shown that the use of a 2D pillar array can enhance the reflectivity of the Bragg reflector. It should be noted that the periodic 2D pillar array can also control the anisotropy of wave propagation along the surface. Owing to this, transverse mode resonances can be suppressed well by adjusting the wave dispersion curve properly.

Ultra-broadband and wide-angle plasmonic absorber based on all-dielectric gallium arsenide pyramid nanostructure for full solar radiation spectrum range

Broadband and plasmonic absorbers (PAs) are key components for numerous applications in the fields of energy harvesting, thermal photonics, optoelectronic devices, and enhanced spectroscopy. In this work, we propose a simple and cost-effective metamaterial plasmonic absorber (MPA) design based on an all-dielectric GaAs pyramid nanostructure for the full solar radiation spectrum range. Simulation results demonstrate that the absorbance of the proposed MPA exceeds 85% in the full solar spectrum range, and it exceeds 90% from 0.25 μm to 3.1 μm with a relative bandwidth of approximately 170.74%, with an absorption peak up to 99% at resonance wavelength. The high absorption is attributed to the excitation of wave-guide mode, surface plasmon polariton (SPP) resonance modes combined with coupling effect and intrinsic lossy of dielectric GaAs and metallic tungsten (W). Furthermore, the proposed MPA is polarization-independent and wide incident angles for both transverse electric (TE) and transverse magnetic (TM) modes. Additionally, the MPA can tolerate certain structural parameter errors during practical fabrication applications. Furthermore, the photophysical properties of this MPA for solar cell applications are investigated, revealing the achievement of high short-circuit current density. Our proposed design is highly promising for applications in solar energy harvesting, thermoelectric, and thermal emitter applications.

Origin of charge density wave in topological semimetals SrAl4 and EuAl4

Topological semimetals in BaAl4-type structure show many interesting behaviors, such as charge density wave (CDW) in SrAl4 and EuAl4, but not the isostructural and isovalent BaAl4, SrGa4, and BaGa4. Here using Wannier functions based on density functional theory, we calculate the susceptibility functions with millions of k-points to reach the small q-vector and study the origin and driving force behind the CDW. Our comparative study reveals that the origin of the CDW in SrAl4 and EuAl4 is the strong electron-phonon coupling interaction for the transverse acoustic mode at small q-vector along the Γ-Z direction besides the maximum of the real part of the susceptibility function from the nested Fermi surfaces of the Dirac-like bands, which explains well the absence of CDW in the other closely related compounds in a good agreement with experiment. We also connect the different CDW behaviors in the Al compounds to the macroscopic elastic properties.

Active Vibration Damping Using Rotor Torque Control in Electric Aircraft

Vibration damping in aerospace structures can decrease the likelihood of failures and instabilities and improve passenger comfort. This paper introduces the novel idea of damping vibration using the electric proprotors on aircraft without compromising flight control. The equations of motion of a cantilevered beam with a propeller at the tip driven by an electric motor are obtained using Hamilton’s principle, solved analytically in the frequency domain, and approximately in the time domain. Feeding back the beam tip angular rate to the motor torque is shown to asymptotically stabilize all transverse beam vibration modes. The overall vibration control consists of the inner rate feedback damping loop with an outer rotor speed control loop. Experimental frequency response and step response validate the models and show that the closed-loop damping in the first mode is three times higher than open loop with less than 1% rotor speed change for a 3% initial tip displacement. Theoretical results give good agreement with experiments. Parametric studies based on a 12 kg quadcopter indicate that if the rotor inertia is sufficiently large the proposed control can provide 8% damping with minimal impact on rotor speed.

Advances in Semiconductor Lasers Based on Parity-Time Symmetry.

Semiconductor lasers, characterized by their high efficiency, small size, low weight, rich wavelength options, and direct electrical drive, have found widespread application in many fields, including military defense, medical aesthetics, industrial processing, and aerospace. The mode characteristics of lasers directly affect their output performance, including output power, beam quality, and spectral linewidth. Therefore, semiconductor lasers with high output power and beam quality are at the forefront of international research in semiconductor laser science. The novel parity-time (PT) symmetry mode-control method provides the ability to selectively modulate longitudinal modes to improve the spectral characteristics of lasers. Recently, it has gathered much attention for transverse modulation, enabling the output of fundamental transverse modes and improving the beam quality of lasers. This study begins with the basic principles of PT symmetry and provides a detailed introduction to the technical solutions and recent developments in single-mode semiconductor lasers based on PT symmetry. We categorize the different modulation methods, analyze their structures, and highlight their performance characteristics. Finally, this paper summarizes the research progress in PT-symmetric lasers and provides prospects for future development.

Requirements on double-cladding Yb-doped fiber for power scaling of diffraction-limited fiber amplifiers.

Requirements on the double-cladding Yb-doped fiber (DCYF) for power scaling of diffraction-limited fiber amplifiers are studied in this paper. By considering the limitations of thermal lens and transverse mode instability separately, it is found that the power scaling limit can be enlarged to more-than 100 kW and 80 kW, respectively, with the proper selection of pump and signal wavelengths. It is also found that the requirements on DCYF strongly depend on the wavelength and brightness of pump light. It is predicted that smaller-than 20-µm core diameter is required to achieve the 20-kW output power, as long as the 976-nm pump brightness can be high enough. The requirements on the inner-cladding diameter and cladding-to-core ratio of DCYF are also investigated.

Manipulation of plasmon dephasing time via the coupling between localized surface plasmon resonance and waveguide modes

Manipulation of plasmon dephasing time of the hybrid modes has gained much attention in recent years, which plays critical roles in many important applications of plasmonics. Here, we manipulate the dephasing time of plasmonic field resulting from coupling of the localized surface plasmon (LSP) of the nanosphere array and the waveguide mode supported by the indium tin oxide film with quasi-normal mode-assisted harmonic oscillator model method. It results in the formation of two distinct modes, transverse electric (TE) and transverse magnetic (TM) modes. Such coupling can significantly modify the dynamics of the original plasmonic modes. The dephasing time of the hybrid plasmon modes, encompassing both TE and TM modes, can be extended from 1.25fs to 4.95fs, which is about 2–7 times compared to that of a single localized surface plasmon resonant mode. More importantly, by changing the structural parameters, we can flexibly manipulate either the dephasing time with a fixed wavelength or the resonant wavelength with a fixed dephasing time.

Transmittance properties of one-dimensional photonic hypercrystals

Our focus in this article lies on the utilization of two distinct hyperbolic metamaterial layers, namely Ag/TiO2 and Ag/Si, within the photonic hypercrystals. Transmission properties are evaluated by the transverse electric and transverse magnetic modes of light using transfer matrix method. In different wavelength regions, we unveil a captivating phenomenon that unfolds the polarization-dependent blueshift and redshift. This dependence is explored through the curve plotting, enabling us to comprehend and appreciate the details of these spectral shifts within the photonic band gaps.

Ultra-compact SOI-based higher-order mode pass wavelength demultiplexer.

We propose an ultra-compact mode filtering wavelength demultiplexer design with a footprint of 3µm×3µm. Our device can route input T E 1 mode signals at 1310nm and 1550nm to different output ports while simultaneously blocking fundamental transverse electric (T E 0) mode input. Our device is designed based on the topology optimization algorithm, which results in an ultra-compact footprint combining wavelength routing and mode filtering functions for the first time, to the best of our knowledge. Our final optimized devices demonstrated insertion losses of 1.26dB and 1.47dB for the C- and O-band output ports, respectively, with inter-port crosstalk as low as -21.25d B and -30.99d B. The extinction ratios between T E 1 mode and T E 0 mode are 24.02dB and 30.12dB at the 1310nm and 1550nm output ports. The combination of small footprint, broad transmission bandwidth, T E 1 to T E 0 mode selectively filtering, and C- and O-band T E 1 mode demultiplexing functions make this a uniquely versatile device that can play an important role in future high density mode-wavelength multiplexing systems.

Spin-controlled topological phase transition in non-Euclidean space

Modulation of topological phase transition has been pursued by researchers in both condensed matter and optics research fields, and has been realized in Euclidean systems, such as topological photonic crystals, topological metamaterials, and coupled resonator arrays. However, the spin-controlled topological phase transition in non-Euclidean space has not yet been explored. Here, we propose a non-Euclidean configuration based on Möbius rings, and we demonstrate the spin-controlled transition between the topological edge state and the bulk state. The Möbius ring, which is designed to have an 8π period, has a square cross section at the twist beginning and the length/width evolves adiabatically along the loop, accompanied by conversion from transverse electric to transverse magnetic modes resulting from the spin-locked effect. The 8π period Möbius rings are used to construct Su–Schrieffer–Heeger configuration, and the configuration can support the topological edge states excited by circularly polarized light, and meanwhile a transition from the topological edge state to the bulk state can be realized by controlling circular polarization. In addition, the spin-controlled topological phase transition in non-Euclidean space is feasible for both Hermitian and non-Hermitian cases in 2D systems. This work provides a new degree of polarization to control topological photonic states based on the spin of Möbius rings and opens a way to tune the topological phase in non-Euclidean space.Graphical abstract

Temperature eigenfunction basis for accelerated transverse mode instability simulation.

This work presents a model for the simulation of transverse mode instability (TMI) in rare earth doped optical fiber amplifiers. The model evaluates the internal temperature of a fiber using a superposition of a finite number of thermal eigenmodes. This simplification greatly enhances the speed of calculation with negligible impact on calculation accuracy. This new method is described and quantitatively compared to an older model that uses standard, spatially resolved FDTD to integrate the heat diffusion equation. When tested over a range of spatial and temporal resolutions, this model reduces runtime by a factor of ∼13.9 on average relative to identical simulations using the spatially resolved model.

Frequency Design of a Vertical Cantilever Beam Carrying Tip Mass

Previous research has revealed that vertical cantilever beam structures, after considering the effects of gravity, can exhibit a 1:3 internal resonance between two transverse modes. However, whether a similar phenomenon would still occur in the system when a proof body is attached to the free end of cantilever beams, and how to perform parameter design to deliberately induce internal resonance are still open issues. The present study conducts research on the natural frequencies of a vertical cantilever beam with a tip mass. Within the framework of the Euler–Bernoulli beam theory, Hamilton’s principle is utilized to derive the integral-partial differential equation of free vibration of the system. The corresponding frequency equation is then solved using the Chebyshev pseudospectral method, with an algebraic equation of the natural frequency obtained. Moreover, an explicit analytical expression for the fundamental frequency is obtained using parameter fitting, which is then used to reveal the relationship among parameters under the critical state of buckling and evaluate the extent of gravity’s impact on the fundamental frequency. The study finally investigates the ratio of the first two natural frequencies. A parameter design method is proposed, which derives a parametric curve in terms of the fundamental frequency, ensuring a 1:3 ratio between the first two natural frequencies. The free vibration time history at the midpoint of the beam is acquired by directly solving the system’s partial differential equation through the finite element method. Fourier transformation of this time history verifies that the fundamental frequency aligns with a predetermined value, and the ratio between the first two natural frequencies is 1:3, thus confirming the efficacy of the proposed method. It is found that the addition of a tip mass provides more flexibility in adjusting parameters to achieve internal resonance, which facilitates the miniaturization of actual structures.

Proposal to Observe Transverse Sound in Normal Liquid $$^3$$He in Aerogel

AbstractIn the Fermi liquid metallic state, a static local magnetic moment is induced on the application of a circularly polarized electromagnetic wave, via the inverse Faraday effect (IFE). The direction of this moment is along the direction of propagation of light, and the magnitude of the moment depends on the frequency of light, the temperature and various material parameters characteristic of the metal. I propose an analogous effect in the Fermi liquid state of $$^3$$ 3 He. A static circulating current is induced when liquid $$^3$$ 3 He is driven by a circularly polarized transverse acoustic wave. For liquid $$^3$$ 3 He filled into aerogel, the coupled system supports a low-attenuation transverse sound mode. I estimate the magnitude of induced circulating currents for this system and find that these are within the range of experimental measurement in the low-attenuation regime. The axis of circulation is along the direction of propagation of the acoustic wave. I propose this analogue of the inverse Faraday effect as a scheme to experimentally demonstrate the propagation of transverse sound in $$^3$$ 3 He-aerogel.

Ultra-thin water-based metasurface with dual-broadband perfect absorption

The rapid development of the 5 G technology can be attributed to its outstanding penetration in the low frequency bands ranging from 600 MHz to 6 GHz, particularly in specific frequency ranges like 700 MHz, 2.3 GHz, and 3.5 GHz. Simultaneously, the technology excels in the millimeter-wave spectrum, spanning from 24 GHz to 52 GHz, notably in bands such as 24.25–27.5 GHz and 37–40 GHz, showcasing impressive capabilities for high-speed data transmission. Nevertheless, these signals frequently encounter electromagnetic interference from electronic equipment in practical applications, which compromise the quality of communication. To address these issues, this paper presents the design, fabrication, and measure of a dual-broadband ultra-thin water-based metasurface absorber (WBMA). The unit cell is composed of a 4 mm thick photoresist shell encasing a water layer and metal plate, and features an irregular octagonal prism and a rectangular annulus cavity within the water layer. Simulation and experimental outcomes indicate that the proposed metasurface achieves near-perfect absorption at frequencies from 4.2 GHz to 4.8 GHz and from 23.6 GHz to 51.1 GHz in the transverse electric mode. Additionally, the proposed metasurface exhibits more than 90% absorption in the transverse magnetic mode for frequency ranges from 4.3 GHz to 4.9 GHz and from 23.2 GHz to 50.8 GHz. The designed water-based metasurface also exhibits features of polarization insensitivity and capability to handle wide-angle incidence. Analysis of the electric and magnetic field distribution within the metasurface suggests that the absorption mechanism is driven by strong magnetic resonance within the water layer’s structure. Furthermore, the effective impedance of the metamaterial absorber is explored. Given the unique absorption frequency bands, the proposed WBMA has potential applications in the realm of 5G communication.

Optical cavity spectroscopy using heterodyne detection with optical feedback laser frequency locking.

We demonstrate an accurate high sensitivity method for cavity spectroscopy. We measure the frequency intervals of transverse electromagnetic modes relative to a fundamental mode in a high finesse optical resonator, and attribute their mode numbers unambiguously. A laser is frequency locked to a fundamental T E M 00 cavity mode by optical feedback, and phase modulation is used to obtain frequency side bands, which may come to resonance with other transverse cavity modes as the radio-frequency of the modulation is tuned. At these resonances, transmission of the side bands is sensitively detected by heterodyning with the carrier. We also analyze the transverse spatial profile of the heterodyne signal for identification of mode numbers. The adjustment of the Gaussian cavity model to the measured frequency intervals yields values of cavity length, mirror radius of curvature, and mirror ellipticity, with high precision to the ppm level.