Waveguide Structure Research Articles

A novel active switchable multi-channel waveguide based on the Bragg scattering mechanism and the force-magnetic coupling effect

PurposeThis study aims to propose a novel acoustic metamaterial waveguide with active switchable channels by changing the magnetic field strength.Design/methodology/approachBased on the Bragg scattering mechanism and the force-magnetic coupling effect of magnetorheological elastomer (MRE), an acoustic metamaterial waveguide structure containing lead scatterers and an MRE/rubber matrix is constructed. By changing the external magnetic field strength, the bandgap of the acoustic metamaterial can be adjusted, and then the channels of the proposed acoustic metamaterial waveguide can be actively switched. The bandgap ranges of acoustic metamaterials containing scatterers with different sizes are different and by designing the size of the scatterers, an acoustic metamaterial waveguide can be formed. The design and control method of this study will be useful for the design of waveguides and active control of bandgaps.FindingsThe proposed switchable multi-channel waveguide and active control method can effectively control the elastic wave propagation, and the opening and closing of the channel are achieved.Practical implicationsThis study provides a new control method for waveguides and expands the application range of MRE. The proposed design concept of adjustable waveguides can be extended for the design of waveguides, metamaterials and vibration reduction structures.Originality/valueThis article proposes a waveguide structure controlled by an external magnetic field in a non-contact manner based on the principle of Bragg scattering and the force-magnetic coupling effect. The model is established, and its feasibility is demonstrated through numerical simulations.

Numerical study of tunable terahertz radiation from differential frequency generation in high-<i>Q</i> geometrically perturbed grating waveguide structures

Nonlinear difference frequency generation (DFG) is a key mechanism for realizing terahertz (THz) sources. Utilization of DFG within micro- and nano-structures can circumvent the phase-matching limitations while supporting device miniaturization and integrability, thus the DFG is made a significant area of research. Enhancing the local electric fields through resonant modes in micro- and nano-structures has become a promising approach to achieving efficient and tunable THz sources across a broad wavelength range. In this work, the mechanism of DFG in high-Q-factor grating-waveguide structures for efficientlytuning THz radiation over a wide spectral range is investigated by using numerical simulations based on the finite element method (COMSOL Multiphysics). Theoretical analysis reveals that modulating the positional perturbation of one of the adjacent gratings effectively doubles the grating period, causing Brillouin zone to fold. This folding shifts the dispersion curve of the guided mode (GM) within the waveguide layer above the light cone, forming a guided mode resonance (GMR) with an ultra-high Q-factor, thereby significantly enhancing THz generation in a broad spectral range. Taking a cadmium sulfide (CdS) grating-waveguide structure for example, numerical simulations demonstrate that the THz conversion efficiency reaches an order of 10<sup>–8</sup>W<sup>–1</sup> when both fundamental frequency beams have an intensity of 100 kW/cm<sup>2</sup>, which is 10<sup>9</sup> times higher than the conversion efficiency of a CdS film of the same thickness. Moreover, the fundamental frequency resonance wavelength can be widely tuned by adjusting the incident angle. High-Q-factor resonance modes enable various fundamental frequency combinations by changing the incident angles of the two fundamental frequency beams, facilitating the generation of THz waves with arbitrary frequencies. This approach ultimately enables a highly efficient and tunable THz source in a wide spectral range, providing valuable insights for generating THz sources on micro- and nanophotonic platforms.

Optical analog to adiabatic passages in two coupled nonlinear waveguides by resonance-locked inverse engineering

Abstract We discuss in this paper the optical analog to rapid adiabatic passage (RAP) and two-state stimulated Raman adiabatic passage (STIRAP) in coupled waveguides with nonlinearity. With the increase of the power of light propagating in waveguides, the nonlinearity can significantly prevent the two adiabatic passages from being successfully simulated. Nevertheless, we find that the negative role of the nonlinearity can be avoided under the assistance of the method of resonance-locked inverse engineering. The method implies redesigning the longitudinally varying detuning of the propagation constants. We further point out that the variation of the detuning does not have to be exactly the same as what the method suggests. As long as the detuning has similar trend to what the method shows, the RAP and two-state STIRAP can still be realized in nonlinear waveguides. This makes the waveguide structure more simpler. Based on our study, the applications of two-state adiabatic passages in designing directional couplers and beam splitters are extended from linear to nonlinear waveguides.

Mathematical model for enhancing midwave infrared transmission using phoxonic crystals

Abstract This paper presents a novel mathematical model for designing a highly efficient on-chip optical waveguide operating in the Mid-Wave Infrared (MWIR) spectrum, specifically covering a range from 3-5μm. The proposed waveguide (called Phoxonic waveguide) architecture achieves exceptional transmission rates of up to 99.8% throughout this broad range of MWIR. The simultaneous control of photon and phonon transmission in the proposed waveguide structure gives its name Phoxonic crystal waveguide. The exceptional performance in the proposed waveguide structure has been achieved due to the innovative use of a mirror-symmetric architecture, which effectively suppresses losses caused by the interaction between photons and phonons. To validate the proposed mathematical model's effectiveness, extensive numerical simulations were conducted using the Qutip platform. This research opens up promising avenues for the development of MWIR waveguides with wide-ranging applications in communication, defense, medicine, and technology.

Design and FDTD simulation of a remote-controllable visible-light plasmonic waveguide and refractive-index-sensitive switch

In this paper, a plasmonic switch based on metal-insulator-metal (MIM) waveguide structure is proposed, whose transmission characteristics can be remotely controlled by a rake switch design. The distance from the remote control unit to the bus waveguide is more than 1 um and still maintains a very high efficiency. The refractive-index-dependent transmission spectrum of this filter was simulated using the finite-difference time-domain method. The results show that the on/off switching of wave propagation in the bus waveguide can be achieved by changing the refractive index of the control unit 1 µm away from the bus waveguide. A change in refractive index of only 0.2 is required to simultaneously control the switching off and on of four waves in the waveguide in the visible band, with corresponding switching ratios of 40.5, 74.3, 48.6, and 15.1, showing great potential for applications in refractive index sensors and remotely controllable band stop filters.

Dual- and triple-band quasi-elliptic bandpass filters based on single-cavity multi-mode hybrid cavities

In this paper, a novel construction method for a single hybrid cavity is proposed for the first time, which integrates a quarter-mode substrate integrated waveguide structure into a patch cavity (QMSIWP), and a novel single-cavity multi-mode resonator is realized through the incorporation of cross-slot lines. A detailed analysis of its characteristics, combined with a specialized feed structure, leads to the design of multiple dual-band quasi-elliptic bandpass filters (BPFs) with varying frequency ratios and a triple-band quasi-elliptic BPF. The finite frequency transmission zeros (FTZs) and bandwidths (BWs) can be controlled by adjusting various parameters. For the demonstration, a triple-band quasi-elliptic BPF is fabricated and measured to validate the performance and design method of the proposed QMSIWP hybrid cavity and feed structure. The measured results agree with the synthesized and simulated results, confirming the proposed method's feasibility and universality. The proposed filter exhibits advantages such as compact size, high selectivity, and excellent group delay, which expands its application prospects and potential value.

Behavior of TE and TM propagation modes in nanomaterial graphene using asymmetric slab waveguide

Abstract In this article, the conduction of transverse electric/transverse magnetic (TE/TM) propagation modes in nanomaterial graphene utilization of asymmetric dielectric slab waveguide was studied in terms of their applicability in optical fiber communication. Nano-graphene film was deposited on silica substrate and air cladding. Three layers were exposed to electromagnetic waves with a 1.55 µm wavelength and 1 µm thick nanographene film, silica, and air covering to study the performance and optical properties of graphene nanomaterials. The models were influenced by factors such as attenuation wavenumbers, cut-off frequency, mode number, propagation wavenumbers, skin depth, and angles of total internal reflection. The impact of these parameters was assessed through numerical analysis, revealing significant correlations. The modes generated ten numbers of TE and nine numbers of TM mode dependent upon the structure of nanographene, with low loss propagation wavenumber. As the TE/TM modes increase, the decay wavenumbers of the cladding and substrate parameters diminish. This indicates that the magnetic and electric fields undergo extremely rapid decay beyond the film region, which leads to the skin depth for higher TE/TM modes traveling longer distances in the cladding and substrate than do lower-order modes. Therefore, nanographene exhibits good optical properties due to its low absorption loss. The angles of internal reflection are greater in magnitude than the substrate and cladding key angles. Still, in the tenth TE mode, the internal reflection angles are extremely close to the critical angle as a result of the small substrate decay parameter and the near operating frequency. The tenth TE mode is weakly characterized. The characteristics of TE/TM modes in an asymmetric three-layer slab waveguide structure are realized for various mode orders and various parameters of nanographene material. The field profiles of the TE/TM modes are submitted to comprehend these characteristics.

Акустические эффекты на волноводных микроструктурах в кремнии

Basic waveguide structures in anisotropic monocrystalline silicon medium are investigated for the existence of localized acoustic modes. The geometries of the structures were determined by technological methods and the practice of anisotropic etching, which guarantees reproducible high-quality structures in terms of geometric and crystallographic parameters. The acoustic effects were modeled by semi-analytical finite element method in the problems on eigenvalues and on the response to a harmonic traction source. Edge and surface localized modes were found. The spectral composition of the localized modes was interpreted on the basis of the surface acoustic wave slowness curves. Pseudomodes, highly localized leakage waves, were detected in a number of considered structures. The obtained results allow to evaluate promising geometrical configurations for further detailed study of the complete scope of dispersion properties of both single waveguides and their finite set.

Ultrahigh-contrast plasmonic mode conversion in coupled graphene waveguides by manipulating the graphene chemical potential and the gyration

We investigate ultrahigh-contrast plasmonic mode conversion in a coupled graphene waveguide structure with manipulated gyration and graphene chemical potential by using both analytic theory and numeric simulations. The ultrahigh contrast is supported by a magnetic resonance at the expense of high sensitivity on the design and material parameters and the operation frequency. The analytical study reveals that the ultrahigh contrast mode conversion can be preserved by adjusting the gyration and the chemical potential in the deviation of structural and material parameter values due to imperfect fabrication and harsh environment and for tuning its operation frequency over a broadband frequency range. We derive explicit analytical results for the resonance gyration and chemical potential that answer to those questions how to manipulate the gyration and the chemical potential according to the design and material parameters and the operation frequency. Numerical simulations demonstrate the robust and broadband tunable plasmonic mode conversion preserves the contrast higher than 103 (99.9%) for different design and material parameter values over a one-octave-spanning broadband frequency range. In practice, the chemical potential and the gyration can be manipulated by controlling the gate voltage of the graphene and the external magnetic field, respectively. Our findings can be of great importance in the design of high-integration nanophotonic circuits and for probing of ultrafast magnetization dynamics. Published by the American Physical Society 2024

Single photon scattering with the giant and small atom interplay in a one-dimensional coupled resonator waveguide

We study single photon scattering in a one-dimensional coupled resonator waveguide, which is dressed by a small and a giant artificial atom simultaneously. Here, we have set the small atom to be a neighbor to one leg of the giant atom, and the giant atom couples to the waveguide via two distant sites. When the small and giant atoms are both resonant with the bare resonator in the waveguide, we observe the perfect reflection of the resonant incident photon. On the other hand, when the small atom is detuned from the giant atom, the single photon reflection is characterized by a wide window and Fano line shape. We hope our work will pave the way for the potential application of small and giant atom hybrid systems in the study of photonic control in the low-dimensional waveguide structure.

A beam-reconfigurable probe-fed mm-wave SIW slot array antenna using cavity-backed U-slot SIW switch

ABSTRACT A beam-reconfigurable millimeter-wave (mm-wave) antenna is proposed, constructed with a dodecagonal substrate integrated waveguide (SIW) structure and a cavity-backed U-slot SIW switch. The SIW switch consists of a U-shaped slot in the ground plane, a p-i-n diode, and a pair of metallic vias, primarily operated by controlling the impedance of the U-shaped slot. Six SIW switches are employed to enable six-beam switchable reconfiguration. Correspondingly, six 4 × 4 SIW slot subarrays are equiangularly arranged along the periphery of the dodecagonal substrate, acting as the main radiators. By carefully controlling the excitation phase and magnitude of the slot elements in the subarrays, a tilted beam of approximately θ = 19° can be produced in measurement with switchable reconfigurable beams 1‒6 steering along the azimuth plane at discrete angles of approximately ϕ = 90°, 150°, 210°, 270°, 330°, and 30°, respectively. The measured results indicate that the overlapped impedance bandwidth (|S11|<-10 dB) of the proposed antenna is across 25.63‒26.08 GHz with a relative bandwidth of 3.7%. The measured antenna peak gains for beams 1‒6 can reach up to 8.0 dBi.

GST and BFO assisted microring resonator for nanoplasmonic applications

In this paper a Metal-Insulator-Metal configuration based electro-optic microring resonator is designed and simulated by using Bismuth Ferrite and Germanium Antimony Telluride for wavelength filtering, switching and modulator applications. The device works on the phenomena of change in refractive index of the active materials when electric field is applied. Initially, switching and filtering is demonstrated by using bismuth ferrite as an active material inside the ring resonator. Later on, an additional layer of GST is added to the ring resonator resulting in increased light confinement inside the ring resonator in the amorphous state of GST layer. Due to this, resonant dips sharpens which improves the quality factor of the device up to 154. By optimizing the device's structural parameters, a modulation depth of 23.11 dB is achieved with a low loss of 1.6 dB. Additionally, these innovative SPPs plasmonic waveguide structures can accommodate various filtering requirements and have good filtering efficiency.

Impact of U-shaped waveguide structures on optical comb generation in microresonator systems

In the research of soliton microcombs, the pump energy conversion efficiency (ECE) of the microcomb is an important parameter. However, in traditional microresonator systems, the ECE is only a few percent. Researchers have enhanced it by introducing additional feedback coupling structures or composite cavity structures into the microresonator system to suppress the output of pump light in the soliton generation region. The additional structures may affect the output comb characteristics of the system, but most articles do not delve into this issue, which hinders the practical application of high-efficiency soliton microcombs. In this paper, we establish rate equations describing the nonlinear dynamics of a microresonator with a U-shaped waveguide feedback coupling structure (coupled-cavity system, CCS), and numerically simulate and conduct steady-state analysis of the simulation results to obtain the influence of the U-shaped waveguide on the CCS’s output comb characteristics. Then we optimize the structural parameters of the CCS reducing the parametric oscillation threshold of the pump by more than 50%, while increasing the ECE to over 25% when the optical field in the microresonator propagates in the form of a single soliton.

Modulation of hybrid plasmon phonon polaritons mode in circular cylindrical three-layer graphene waveguide

In this present research article, we have investigated analytically the characteristics of the fundamental mode of hybrid surface plasmon phonon polariton (HSPPhPs) mode in a circular cylindrical three-layer graphene (CTLG) waveguide structure. The dispersion equation of HSPPhPs is derived by using Maxwell’s equations and continuity conditions of tangential components of electric and magnetic fields in cylindrical geometry. The dispersion curve has been illustrated and thoroughly examined in relation to the effects of temperature and chemical potential (μc) of graphene, as well as variations in the thickness of silicon dioxide (SiO2) and hexagonal boron nitride (hBN) layers, and found that in the presence of hBN, the effective mode index exhibits hyperbolic behavior with wave number. Up to the first Reststrahlen band (∼830.57 cm⁻¹), it varies slightly with graphene temperature; increasing graphene's (μc) lowers the index, while a thicker hBN layer reduces it, whereas the index increases with SiO₂ layer thickness. Also, we looked at how the CTLG waveguide structure is affected by the electric field distribution, phase speed, and propagation length.

Sub-picosecond mode-locked laser operation in a femtosecond-laser-inscribed Yb:CaF2 channel waveguide

We present the successful demonstration of both Q-switched mode-locked (QSML) and continuous-wave mode-locked (CWML) operation in a femtosecond-laser-inscribed Yb:CaF2 double-track waveguide (WG) structure. A semiconductor saturable absorber output coupler (SOC) was used as the mode locker with fine tuning of the intracavity group delay dispersion (GDD) achieved through the Gires-Tournois interference (GTI) effect induced by an air gap. To ensure sufficient fluence on the saturable absorber, the cavity was extended to 50 cm by inserting two lenses between the SOC and WG, resulting in a repetition frequency of ∼300 MHz. In the QSML regime, the laser exhibited an amplitude modulation period of 65 kHz within Q-switched pulses of 3-µs duration. Notably, in the purely CWML regime, the laser generated a maximum output power of 51 mW near 1036 nm with a pulse width of 979 fs.

Optimization and multiphysics analysis of high-performance lithium niobate modulators

Thin-film lithium niobate electro-optic modulators (TFLN EOMs) are widely utilized across various fields due to their exceptional performance. In this theoretical study, we optimized a TFLN EOM featuring a multimode interference coupler, cosine-curved waveguides, and a modulating arm straight waveguide structure. By tuning the etching depth, waveguide width, and geometric parameters of the traveling wave electrodes, we achieved a half-wave voltage-length product of 1.6V⋅cm and a 3 dB bandwidth of approximately 140 GHz. Additionally, we performed a multiphysics analysis to investigate the temperature characteristics of the modulator. The results indicate that increased temperature induces thermal-optic effects in the material, leading to changes in the waveguide’s refractive index and the optical beam phase, which results in increased insertion loss. Moreover, the stress generated by thermal expansion is concentrated in the modulator’s waveguide, representing a weak point that is prone to failure.

Wide band high gain modified-folded-wave-guide slow wave structure for millimeter-wave traveling wave tube amplifier in 6G and beyond back-haul communications

Abstract Millimeter-wave technology is crucial in telecommunications as it enables higher bandwidths and faster data transfer. V-band represents frequencies ranging from 50 to 75 GHz and is used for short-range back-haul communication, defense radar, inter-satellite communications, and space debris detection. Folded waveguide slow-wave structures (FWG-SWS) are an excellent choice for V-band amplifiers due to their wide bandwidths, large gain, and ease of fabrication using modern lithographic processes. This article presents a modified folded waveguide slow-wave structure (MFW-SWS) for V-band traveling wave tube amplifiers (TWTAs) desirable for multi-gigabit 6G and beyond back-haul communications. The MFW slow-wave structure is an FWG-SWS variant that supports an increased RF phase velocity, accommodating additional SWS length for much-improved amplification. The dispersion analysis effectively provides a 15% operational bandwidth ranging from 64–74 GHz with a reduced phase velocity of three-tenths the speed of light apt for enhanced beam-wave interactions. The two-section SWS has independent attenuators designed to provide over 20 dB attenuation throughout the functional bandwidth effortlessly. Additional wave-guide transitions are introduced to achieve the best attenuation characteristics. Along the axis of the SWS, a square beam tunnel is employed to support a 26 kV round electron beam with a beam current of 70 mA. To contain the electron beam within the beam tunnel, this study used a focusing mechanism with a constant magnetic field of 0.25T, which is highly appropriate for miniaturization and large-scale implementation in 6G back-haul towers. Particle-in-cell (PIC) simulations were performed using the CST (Computer Simulation Technology) Studio Suite, and a gain of over 26 dB with an output power of 50 W was successfully attained across the operational bandwidth.

Numerical simulation and dispersion inversion of ground penetrating radar waveguide

Abstract Ground penetrating radar (GPR) is widely used in near-surface detection due to its non-destructive and high-efficiency advantages. Radar waves are continuously reflected in the waveguide structure, and dispersion will be formed. In order to find out the propagation regularity and characteristics of radar waves in waveguides, we use the simulation and field GPR waveguide data to test the radar wave dispersion characteristic. Then, the Dix-type inversion method is used to estimate the permittivity from the radar wave dispersion curve. The synthetic and field data tests show that the GPR waveguide dispersion inversion can accurately estimate the permittivity result.

Study of the Dispersion Compensation Double-Layer Diffractive Optical Components Based on Metasurface and Grating, and Their Application in Augmented Reality Displays.

We employed a double-layer coupled diffractive optical element, based on metasurfaces and diffraction gratings, which exhibits wavefront modulation and chromatic dispersion compensation. Utilizing this double-layer coupled diffractive optical element in the optical information transmission process of a diffractive waveguide allows for the transmission of color image information using a single-layer waveguide structure. Our results demonstrate that, under the conditions of a field of view of 47° × 47°, an entrance pupil size of 2.9 × 2.9 mm2, and an exit pupil extension size of 8.9 mm, the uniformity of the brightness for each monochromatic field reached 85%, while the uniformity of color transmission efficiency exceeded 95%.

Compact circularly polarized metasurface antenna based on characteristic mode analysis

AbstractThis article introduces a novel, single‐layer, low‐profile, circularly polarized metasurface antenna. Through characteristic mode analysis, the optimization of a 33 rectangular metasurface structure was performed. Two orthogonal modes were selected as the operating modes, and improvements to the metasurface structure were made to achieve a 90 phase difference between these modes. The adoption of a coplanar waveguide structure enables the excitation of the metasurface, facilitating circularly polarized radiation performance for the two selected modes. The antenna's dimensions are 40 mm 40 mm 3 mm (0.67 0.67 0.05 ), featuring a −10 dB impedance bandwidth of 27.8% (4.49–5.94 GHz). The 3 dB axial ratio bandwidth is 14.2% (5.25–6.05 GHz), with a maximum gain of 7.26 dBi.