Higher Order Modes Research Articles

Millimeter-wave wideband filtering on-chip antenna based on IPD technology

ABSTRACT A millimeter-wave wideband filtering on-chip antenna is proposed in this paper. Its operation frequency covers 32 GHz to 63 GHz, and the impedance fractional bandwidth reaches 63%. Based on the corner-fed patch antenna, the antenna in this work has a quasi-omnidirectional radiation pattern, and peak efficiency reaches 91.7%. By square slotting on the four sides of the patch and cross slotting on the center of the patch, the high-order mode is suppressed, which supports the wide operating frequency range with filtering characteristics. Split ring resonators are etched on the ground to strengthen filtering characteristics. Based on thin-film integrated passive device (IPD) technology, the proposed structure is applicable to the on-chip wideband and high-efficiency antenna array.

Dead Zone Fault Detection Optimization Method for Few-Mode Fiber Links Based on Unexcited Coupled Higher-Order Modes

Dead Zone Fault Detection Optimization Method for Few-Mode Fiber Links Based on Unexcited Coupled Higher-Order Modes

Identifying high-order plasmon modes in silver nanoparticle over mirror configuration

Identifying high-order plasmon modes in silver nanoparticle over mirror configuration

Adjoint Algorithm Design of Selective Mode Reflecting Metastructure for BAL Applications

Broad-area lasers (BALs) have found applications in a variety of crucial fields on account of their high output power and high energy transfer efficiency. However, they suffer from poor spatial beam quality due to multi-mode behavior along the waveguide transverse direction. In this paper, we propose a novel metasurface waveguide structure acting as a transverse mode selective back-reflector for BALs. In order to effectively inverse design such a structure, a digital adjoint algorithm is introduced to adapt the considerably large design area and the high degree of freedom. As a proof of the concept, a device structure with a design area of 40 × 20 μm2 is investigated. The simulation results exhibit high fundamental mode reflection (above 90%), while higher-order transverse mode reflections are suppressed below 0.2%. This is, to our knowledge, the largest device structure designed based on the inverse method. We exploited such a device and the method and further investigated the device’s robustness and feasibility of the inverse method. The results are elaborately discussed.

Safety First: Stability and Dissipation of Line-tied Force-free Flux Tubes in Magnetized Coronae

Magnetized plasma columns and extended magnetic structures with both footpoints anchored to a surface layer are an important building block of astrophysical dissipation models. Current loops shining in X-rays during the growth of plasma instabilities are observed in the corona of the Sun and are expected to exist in highly magnetized neutron star magnetospheres and accretion disk coronae. For varying twist and system sizes, we investigate the stability of line-tied force-free flux tubes and the dissipation of twist energy during instabilities using linear analysis and time-dependent force-free electrodynamics simulations. Kink modes (m = 1) and efficient magnetic energy dissipation develop for plasma safety factors q ≲ 1, where q is the inverse of the number of magnetic field line windings per column length. Higher-order fluting modes (m > 1) can distort equilibrium flux tubes for q > 1 but induce significantly less dissipation. In our analysis, the characteristic pitch μ˜0 of flux-tube field lines determines the growth rate ( ∝μ˜03 ) and minimum wavelength of the kink instability ( ∝μ˜0−1 ). We use these scalings to determine a minimum flux tube length for the growth of the kink instability for any given μ˜0 . By drawing analogies to idealized magnetar magnetospheres with varying regimes of boundary shearing rates, we discuss the expected impact of the pitch-dependent growth rates for magnetospheric dissipation in magnetar conditions.

Triple-band transparency effect by multiple couplings based on toroidal dipole resonance

We explored multiple couplings properties in composite metastructure. One part is the asymmetric double rings, supporting the narrow toroidal dipole resonance, and the other component is an upright rod that excites the broad electric dipole resonance. When these two resonant modes coincide in the spectrum, dual-band plasmon induced transparency (PIT) behavior can be obtained, which is attributed to in-phase and out-of-phase couplings between the toroidal dipole and electric dipole modes. Meanwhile, the dual-band features will become a single PIT band by varying the rotation offset angle between the upper- and lower-rings. Moreover, by introducing lateral displacement of the rod with respect to the toroidal component, a triple-band PIT effect can be achieved. In particular, under a large lateral displacement, a broadband transparency window appears across a wavelength range greater than 120 nm, where the transmission exceeds 0.9. It is derived from the hybrid coupling between toroidal dipole, electric dipole and induced high-order resonance modes. The toroidal-based PIT metamaterials not only promote the understanding of toroidal dipole moment but also provide a positive reference for toroidal-based meta-devices.

Circular Differential Photocurrent Mapping of Hot Electron Response from Individual Plasmonic Nanohelicoids.

Chiral plasmonic nanocrystals have recently attracted increasing attention in circular polarization-dependent photocatalysis driven by hot carriers. While being concealed in traditional ensemble measurements, the individual chiral photocatalytic activity of nanocrystals can exclusively be revealed by directly correlating the circular differential photocurrent response to helical morphologies using single-particle techniques. Herein, we develop a method named circular differential photocurrent mapping (CDPM) and demonstrate that CDPM can be used to characterize the circular differential hot electron (CDHE) response from individual Au nanohelicoids (AuNHs) on a TiO2 photoanode in a photoelectrochemical cell. The single-particle circular differential scattering and CDHE measurements were interpreted with calculations performed on a model in direct correlation to the helical morphologies of the nanocrystal. While CDHE response was found inactive at a dipolar resonance of 750 nm, helicity-convoluted sites of HE generation were identified on the AuNH at a specific higher-order mode of 550 nm, resulting in a significant response of CDHE in association with the handedness of the AuNH. Details of circular differential contributions were further resolved by examining the efficiencies of individual AuNHs in terms of g-factors. Our study provides a powerful microscopic method at the single-particle level for the photocatalytic characterization of chiral nanocrystals, gaining fundamental insights into the photocatalysis of chirality, especially toward plasmon-induced asymmetrical photochemistry or photoelectrochemistry.

Dominance of polarization modes and absorption on self-focusing of laser beams in collisionless magnetized plasma

This work investigates the polarization modes i.e., Extraordinary (E-mode) and Ordinary (O-mode) on self-focusing of higher-order mode of elegant Hermite-cosh-Gaussian (EHChG) laser beams within collisionless magnetized plasma medium. In this study, the authors have taken transverse electromagnetic ([Formula: see text]) mode with mode indices (0, 4) and explored. The ponderomotive force is primarily responsible for the dielectric constant’s nonlinearity in this context. Also, WKB and paraxial approximations via the parabolic wave equation approach are used to establish the general form of differential equations for beam-width parameters in both transverse dimensions of the beam. In this paper, the authors have theoretically investigated the dominance of polarization modes and absorption coefficient on self-focusing. The final results show good enhancement of laser propagation through collisionless plasma medium.

Front glass crack inspection of thin-film solar photovoltaic modules using high-order ultrasonic Lamb waves

Ensuring the structural integrity of solar photovoltaic modules is crucial to maintain power production efficiency and fulfill the anticipated product lifespan. Hence, implementing quality control procedures and structural health monitoring is necessary throughout the stages of manufacture and operation. The ultrasonic examination has some benefits compared to electroluminescence and infrared approaches, namely in identifying mechanical flaws in the front glass. The Lamb waves (LW) method is an auspicious inspection approach among ultrasonic-based methods. This is primarily attributed to its quicker measurement speed than the standard ultrasonic c-scan. The LW method offers an advantage in terms of its ability to provide long-range coverage. The predominant approach in LW inquiry often centers on using fundamental modes within the low-frequency range. Nevertheless, the findings of this investigation demonstrate that the higher-order mode exhibits superior effectiveness for the specific objective of this research, as it displays a higher level of sensitivity towards cracks in the front glass of the module. The current study ultimately showcases the use of the LW scan. A damage indication threshold is determined by the fraction of energy spectral density (ESD) associated with the crack-sensitive mode. This technology effectively produces a comprehensive map of the designated area by comparing the ESD values at various measurement positions with a predetermined threshold. This map provides precise indications of the existence of areas that are affected by cracks.

Mode-Locked Operation of High-Order Transverse Modes in a Vertical-External-Cavity Surface-Emitting Laser

Understanding the mechanism of mode-locking in a laser with high-order transverse mode is important for achieving an ultrashort pulses train under more complicated conditions. So far, mode-locking with high-order transverse mode has not been reported in other lasers except the multimode fiber laser. This paper demonstrates robust mode-locking with high-order transverse mode in a Kerr-lens mode-locked vertical-external-cavity surface-emitting laser for the first time, to the best of our knowledge. While the longitudinal modes are locked, continuous mode-locking accompanied by high-order transverse mode up to TEM40 is observed. The threshold of the mode-locking is only a little bigger than that of the lasing. After the laser oscillation is built up, the mode-locked pulse train can be obtained almost immediately and maintained until the thermal rollover of the laser. Output powers of 717 mW under fundamental mode and 666 mW under high-order transverse mode are achieved with a 4.3 ps pulse duration and 1.1 GHz pulses repetition rate, and some phenomenological explanations to the related characteristics of the mode-locked operation of high-order transverse mode in the vertical-external-cavity surface-emitting laser are proposed.

Early-Stage Ice Detection Utilizing High-Order Ultrasonic Guided Waves

Ice detection poses significant challenges in sectors such as renewable energy and aviation due to its adverse effects on aircraft performance and wind energy production. Ice buildup alters the surface characteristics of aircraft wings or wind turbine blades, inducing airflow separation and diminishing the aerodynamic properties of these structures. While various approaches have been proposed to address icing effects, including chemical solutions, pneumatic systems, and heating systems, these solutions are often costly and limited in scope. To enhance the cost-effectiveness of ice protection systems, reliable information about current icing conditions, particularly in the early stages, is crucial. Ultrasonic guided waves offer a promising solution for ice detection, enabling integration into critical structures and providing coverage over larger areas. However, existing techniques primarily focus on detecting thick ice layers, leaving a gap in early-stage detection. This paper proposes an approach based on high-order symmetric modes to detect thin ice formation with thicknesses up to a few hundred microns. The method involves measuring the group velocity of the S1 mode at different temperatures and correlating velocity changes with ice layer formation. Experimental verification of the proposed approach was conducted using a novel group velocity dispersion curve reconstruction method, allowing for the tracking of propagating modes in the structure. Copper samples without and with special superhydrophobic multiscale coatings designed to prevent ice formation were employed for the experiments. The results demonstrated successful detection of ice formation and enabled differentiation between the coated and uncoated cases. Therefore, the proposed approach can be effectively used for early-stage monitoring of ice growth and evaluating the performance of anti-icing coatings, offering promising advancements in ice detection and prevention for critical applications.

Design and operation results of KSTAR ECH system

The electron cyclotron heating (ECH) system at the Korea Superconducting Tokamak Advanced Research (KSTAR) is a crucial heating devices, which is employed in various research endeavors, including plasma startup, wall cleaning, neoclassical tearing mode control, long pulse operation, and hybrid scenarios development from the first plasma operation. For facilitating advanced scenarios development and magnetohydrodynamics research in KSTAR, it was deemed necessary to install a total of 6 MW ECH systems, consisting of four 105/140 GHz and two 170 GHz systems. To address this, a new ECH room was developed and the existing ECH system was totally rearranged. This study describes the design of the novel KSTAR ECH system and its operation results, and discusses the problems that occur during the ECH system operation. Each ECH system to deliver 1 MW for 300 s was designed to enable stable, safe, and efficient operation in the new ECH room and four 105/140 GHz dual frequency ECH were injected to KSTAR successfully. The polarization angle was experimentally confirmed by using an electron cyclotron wall conditioning, and the beam angle change by ECH antenna was verified by a newly developed IR measurement. However, mixed patterns with higher-order modes were observed in the output beam from matching optics unit of some gyrotrons, which affect the operation efficiency and the output power. In future works, we will analyze the causes for low mode purity and improve the operation efficiency.

Orthogonal multi-peak solitons from the coupled fractional nonlinear Schrödinger equation

In this paper, we investigate the dynamics and stability of multi-peak solitons from the coupled nonlinear Schrödinger equation with the fractional dimension based on Lévy random flights. By implementing linear stability analysis and direct simulations, we demonstrate regions where the single and multi-peak modes are stable. Analysis of perturbed coupled solitons confirms the stability of higher-order modes compared to lower-order modes under the same configurations. The stability diagrams show that the force coupling, Lévy index, power, and the nonlinear intensity significantly influence the stability of high-order modes. Our findings indicate that stability is favored in self-defocusing systems with high Lévy indices under weak coupling conditions, with higher-order states exhibiting smaller stability regions.

Compact adiabatic mode (de)multiplexer using a subwavelength grating waveguide in the silicon-on-insulator platform

Mode-division multiplexing technology holds great promise for addressing the ever-increasing demand for data transmission capacity. This paper proposes a compact adiabatic mode (de)multiplexer [(de)MUX] using a subwavelength grating (SWG) waveguide in the silicon-on-insulator platform, with optimization for the TE0-TE1 and TE0-TE2 mode (de)MUXs. By introducing an SWG waveguide, the coupling strength of waveguides can be enhanced, making it possible for the realization of more compact adiabatic mode (de)MUXs. The adiabatic evolution lengths for TE0-TE1 and TE0-TE2 mode (de)MUXs are only 10 µm and 17.5 µm, respectively. The numerical simulation shows that the operating bandwidth of the proposed device is beyond 200 nm. For the TE0-TE1 mode (de)MUX, the insertion loss and mode crosstalk of TE0-TE1 mode conversion within the whole wavelength range of 1450–1650 nm are less than 0.25 dB and −32.0dB, respectively. For the TE0-TE2 mode (de)MUX, the insertion loss and mode crosstalk of TE0-TE2 mode conversion within the entire bandwidth are less than 0.26 dB and −27.4dB, respectively. The TE0-TE1 and TE0-TE2 mode (de)MUXs can be cascaded to form a three-mode (de)MUX. For TE0-TE0, TE0-TE1, and TE0-TE2 processes within the entire bandwidth, the mode crosstalks are less than −33.5dB, −26.1dB, and −25.8dB, respectively. The device is scalable to the conversion of TE0 mode to higher-order mode.

Delivery of nanosecond laser pulses by multi-mode anti-resonant hollow core fiber at 1 µm wavelength

In this paper we explore the application of low-loss multimode anti-resonant hollow-core fiber (MM-AR-HCF) in the delivery of nanosecond laser pulses at 1 µm wavelength. MM-AR-HCF with large core offers a rich content of low-loss higher-order modes which plays a key role in the efficient coupling and transmission of high-power laser of low beam quality. In the experiment, laser pulses of an average pulse energy of 21.8 mJ with 14.6 ns pulse width (corresponding a peak power of 1.49 MW) are transmitted through MM-AR-HCF of 9.8 m length without damage. 85% transmission efficiency is achieved where the incident laser beam suffers a low beam quality with M2x and M2y of 2.18 and 1.99 respectively. Laser-induced damage threshold (LIDT) of MM-AR-HCF was measured to be 22.6 mJ for 85% transmission efficiency, which is 7 times higher than that for a multimode silica optical fiber with a large core of 200 µm.

Analysis of propagation and resonance properties of longitudinal leaky surface acoustic wave on LiNbO3/SiC bonded structure

Abstract The propagation and resonance properties of longitudinal leaky surface acoustic waves (LLSAW) on a bonded structure comprising an X-cut LiNbO3 (LN) thin plate and a 4H-SiC support substrate are theoretically investigated. The strong LLSAW responses with high Q factors were obtained at the LN thin-plate thickness h where the LLSAW phase velocity was slower than the bulk shear wave of 4H-SiC of 7126 m/s, and a fractional bandwidth (FBW) of 9–10% was obtained for the normalized Al film thickness by wavelength h Al/λ = 0.06–0.07 and h/λ = 0.30–0.40. Moreover, even at h/λ with a faster phase velocity than the bulk shear wave of 4H-SiC, the strong LLSAW responses without spurious response owing to the LLSAW higher-order mode were obtained. Finally, h Al/λ = 0.031 and h/λ = 0.19 were extracted to obtain a phase velocity of 7800 m/s, high Q factors, and FBW of 7.6%.

Design of optical telescopes for laser field wavefront reconstruction in gravitational-wave detectors

Pick-off beams in Interferometric Gravitational Wave Detectors are often used to derive information on the field circulating in the interferometer. In order to retrieve the wavefront of the field at some chosen location, an optical system has to be deployed so to image the desired field characteristics to an optical bench and ultimately to suitable sensors. In this paper, we detail the requirements in terms of Gouy Phase and ABCD matrix for such an optical system to provide the correct information. We show also that by designing the optical system with adequate Gouy Phase evolution, the same kind of transformation holds true not only for the fundamental Gaussian mode, but also for both even and odd Higher Order Modes (HOMs) of the main interferometer beam. This is important because these HOMs are excited by the aberrations of the optical elements in the interferometer, and carry the information one is interested to. Simulations with two tools (Finesse and Zemax OpticsStudio®) are provided to confirm the analytical results obtained using Gaussian modes expansion of a generic field.

Coupling of Modes in Step-Index Plastic Optical Fibers by Using D-Shape Technique

This article presents a technique for reducing the stabilization length of steady-state modes in step-index plastic optical fibers (POFs), which is significant for sensor networks, Internet of Things, signal processing, and data fusion in sensor systems. The results obtained with the com- putational tool developed suggest that the D-shape created in the POF effectively reduces the stabi- lization length of the modes and, by extension, minimizes the dispersion effects of the modes by filtering out high-order modes. Applying the analysis to commercial POFs, the authors experimen- tally verified a reduction in the stabilization length of modes from 27 to 10 m and from 20 m to 5 m. Reducing the mode stabilization length minimizes the bit error rate (BER) in short-length SI-POF- based optical links operating at 250 Mbp/s. A reduction from 7.6 × 10−7 to 3.7 × 10−10 was achieved.

Design and characterization of a self-matching photonic lantern for all few-mode fiber laser systems

We model and demonstrate a self-matching photonic lantern (SMPL) device, which is designed to address the constraint of limited transverse modes generated by fiber lasers. The SMPL incorporates a FMF into the array at the input end of a traditional photonic lantern. The few-mode fiber at the output end is specifically configured to align with the few-mode fiber at the input, therefore named as SMPL. This paper details the design and fabrication of the SMPL device, validated by both simulation and experiment. The 980nm fundamental mode, injected via 980nm single-mode fibers, selectively excites corresponding higher-order modes at the few-mode port of the SMPL. Additionally, 1550nm fundamental and higher-order modes injected at the input end into the SMPL device demonstrates mode preservation and low-loss transmission characteristics. The SMPL is well-suited for developing a ring laser system, enabling selective excitation of 980nm pump light modes and facilitating closed-loop oscillation and transmission of 1550nm laser.

Mode-dependent analysis of a fiber optic curvature sensor with sensitive zone

In this paper, mode-dependent analysis of fiber optic curvature sensor with precision machined structural imperfections (teeth) as sensitive zone is conducted. Using controlled input or light source launching conditions sensor response is measured for different modes excited in the multimode optical fiber. Study shows that as curvature changes there is significant difference in how sensitive zone affects low and high order modes propagating through the fiber. Obtained measurement results provide further insight into FOCS response and open possibilities for development of new measurement approaches which represent a significant step forward for FOCS based measurement systems. Guidelines for maximizing sensor sensitivity, increasing measurement reliability and even avoiding intensity based measurement by measuring changes in the width of the sensor’s output light intensity distribution are discussed in this work.