Optical Modes Research Articles

Mode-division multiplexing for visible photonic integrated circuits.

Visible wavelength photonic integrated circuits (PICs) are critical for a wide range of applications including quantum photonics, high-resolution imaging, optogenetics, and portable displays. These applications require functions such as wavefront structuring and dense optical routing on-chip to serve as compact optical interfaces for qubits and cells. The transverse spatial modes of a waveguide can provide the basis for these functions. However, the excitation of these modes in visible PICs has been limited due to fabrication challenges at shorter wavelengths. Here we demonstrate mode-division multiplexing of three higher-order waveguide modes at visible wavelengths (473 nm) with low crosstalk for the first time, to our knowledge. We use adiabatic linearly tapered asymmetric directional couplers that have high theoretical bandwidths of greater than 100 nm and fabrication tolerance to width variations of greater than 45 nm for future integration into large-scale visible PICs with operation across the red, blue, and green spectrum.

Minimizing Defects in Additive Manufacturing and Laser Welding Through Energy Coupling Experiments and Dynamic Modelling

Additive manufacturing is a revolutionary technology that produces complex components as a single piece, replacing traditional assemblies and reducing waste. Laser powder bed fusion, a type of additive manufacturing, allows for limitless design freedom by building intricate parts layer-by-layer through melting and fusing metal powder. However, build quality remains inconsistent, with deformations like pores and spattering occurring. To improve modelling of the behaviour of melted metal, thus minimizing defects, an experiment which determined the metal’s absorptance of laser energy through integrating sphere radiometry was conducted. The integrating sphere, which spatially integrated a fraction of measured light to calculate full radiance, had to sit above the build plate and not interfere with powder spreading. I designed two parts which attached the integrating sphere to the motorized powder spreading blade. Utilizing small ridges in the enclosure as weight-bearing tracks, the blade’s torque was reduced while allowing precise movement of the sphere. Through implementing these parts, the experiment was conducted, whose results will aid in our understanding of laser-metal interactions. Defects like spattering also occur during laser welding, due to the vaporization of unstable liquid metal. To combat this, novel beam shapes have been seen to increase the stability of the keyhole. To model this effect, I created a phenomenological, dynamic model of the keyhole depth during a copper weld. Two differential equations were created to model the keyhole depth’s rate of change using a dual mode and single mode laser, depending on absorptance and incident laser intensity. The dynamic depth of the keyhole for both modes was numerical solved in Python and iterated using existing copper weld data. Through better quantitative understanding of energy coupling and numerical modelling of the resulting dynamics, defects in laser welding and additive manufacturing can be minimized.

New method for the investigation of mode coupling in graded-index polymer photonic crystal fibers using the Langevin stochastic differential equation

The mode coupling in a graded-index polymer photonic crystal fiber (GI PPCF) with a solid core has been investigated using the Langevin equation. Based on the computer-simulated Langevin force, the Langevin equation is numerically integrated. The numerical solutions of the Langevin equation align with those of the time-independent power flow equation (TI PFE). We showed that by solving the Langevin equation, which is a stochastic differential equation, one can successfully treat a mode coupling in GI PPCFs, which is an intrinsically stochastic process. We demonstrated that, in terms of effectiveness, the Langevin equation is preferable compared to the TI PFE. The GI PPCF achieves the equilibrium mode distribution (EMD) at a coupling length that is even shorter than the conventional GI plastic optical fiber (POF). The application of multimode GI PCFs in communications and optical fiber sensor systems will benefit from these findings.

Analysis of Global and Key PM2.5 Dynamic Mode Decomposition Based on the Koopman Method

Understanding the spatiotemporal dynamics of atmospheric PM2.5 concentration is highly challenging due to its evolution processes have complex and nonlinear patterns. Traditional mode decomposition methods struggle to accurately capture the mode features of PM2.5 concentrations. In this study, we utilized the global linearization capabilities of the Koopman method to analyze the hourly and daily spatiotemporal processes of PM2.5 concentration in the Beijing–Tianjin–Hebei (BTH) region from 2019 to 2021. This approach decomposes the data into the superposition of different spatial modes, revealing their hierarchical spatiotemporal structure and reconstructing the dynamic processes. The results show that PM2.5 concentrations exhibit high-frequency cycles of 12 and 24 h, as well as low-frequency cycles of 124 and 353 days, while also revealing spatiotemporal modes of growth, recession, and oscillation. The superposition of these modes enables the reconstruction of spatiotemporal dynamics with a mean absolute percentage error (MAPE) of only 0.6%. Unlike empirical mode decomposition (EMD), Koopman mode decomposition (KMD) method avoids mode aliasing and provides a clearer identification of global and key modes compared to wavelet analysis. These findings underscore the effectiveness of KMD method in analyzing and reconstructing the spatiotemporal dynamics of PM2.5 concentration, offering new insights into the understanding and reconstruction of other complex spatiotemporal phenomena.

Two-Stage Hyperelliptic Kalman Filter-Based Hybrid Fault Observer for Aeroengine Actuator under Multi-Source Uncertainty

An aeroengine faces multi-source uncertainty consisting of aeroengine epistemic uncertainty and the control system stochastic uncertainty during operation. This paper investigates actuator fault estimation under multi-source uncertainty to enhance the fault diagnosis capability of aero-engine control systems in complex environments. With the polynomial chaos expansion-based discrete stochastic model quantification, the optimal filter under multi-source uncertainty, the Hyperelliptic Kalman Filter, is proposed. Meanwhile, by treating actuator fault as unknown input, the Two-stage Hyperelliptic Kalman Filter (TSHeKF) is also proposed to achieve optimal fault estimation under multi-source uncertainty. However, considering that the biases of the model are often fixed for the individual, the TSHeKF-based fault estimation is robust and leads to inevitable conservativeness. By adding the additional estimation of the unknown deviation in state function caused by probabilistic system parameters, the hybrid fault observer (HFO) is proposed based on the TSHeKF and realizes conservativeness-reduced estimation for actuator fault under multi-source uncertainty. Numerical simulations show the effectiveness and optimality of the proposed HFO in state estimation, output prediction, and fault estimation for both single and multi-fault modes, when considering multi-source uncertainty. Furthermore, Monte Carlo experiments have demonstrated that the HFO-based optimal fault estimation is less conservative and more accurate than the Two-stage Kalman Filter and TSHeKF, providing better safety and more reliable aeroengine operation assurance.

Gouy Phase Induced Optical Skyrmion Transformation in Diffraction Limited Scale

AbstractOptical skyrmions are topologically stable quasiparticles that can be constructed with electric field, spin angular momentum, polarization Stokes vector, pseudospin, etc. In this letter, both theoretical and experimental studies are carried out to reveal the role of Gouy phase in the topology transformation during the tight focusing of Stokes skyrmions. The Stokes skyrmionic beam can be constructed by superposing two orthogonally polarized components with orthogonal spatial modes. The Gouy phase produced in the focused field depends on the orbital angular momentum carried by the high order mode component of the incident Stokes skyrmionic beam. While the beam size of the focused field is diffraction limited, the variation of the Stokes vectors in the skyrmion topology is in the sub‐diffraction limited scale. The presented results shed light on the understanding of the topology transformation between the incident and the tightly focused fields, paving the way for engineering the optical skyrmions in micro‐nano scale and their applications in information processing, quantum technology, metrology, etc.

Deterministic photon source of genuine three-qubit entanglement

Deterministic photon sources allow long-term advancements in quantum optics. A single quantum emitter embedded in a photonic resonator or waveguide may be triggered to emit one photon at a time into a desired optical mode. By coherently controlling a single spin in the emitter, multi-photon entanglement can be realized. We demonstrate a deterministic source of three-qubit entanglement based on a single electron spin trapped in a quantum dot embedded in a planar nanophotonic waveguide. We implement nuclear spin narrowing to increase the spin dephasing time to T2*≃33\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{2}^{*}\\simeq 33$$\\end{document} ns, which enables high-fidelity coherent optical spin rotations, and realize a spin-echo pulse sequence for sequential generation of spin-photon and spin-photon-photon entanglement. The emitted photons are highly indistinguishable, which is a key requirement for scalability and enables subsequent photon fusions to realize larger entangled states. This work presents a scalable deterministic source of multi-photon entanglement with a clear pathway for further improvements, offering promising applications in photonic quantum computing or quantum networks.

MicroMagnetic.jl: A Julia package for micromagnetic and atomistic simulations with GPU support

Abstract MicroMagnetic.jl is an open-source Julia package for micromagnetic and atomistic simulations. Using the features of the Julia programming language, MicroMagnetic.jl supports CPU and various GPU platforms, including NVIDIA, AMD, Intel, and Apple GPUs. Moreover, MicroMagnetic.jl supports Monte Carlo simulations for atomistic models and implements the nudged-elastic-band method for energy barrier computations. With built-in support for double and single precision modes and a design allowing easy extensibility to add new features, MicroMagnetic.jl provides a versatile toolset for researchers in micromagnetics and atomistic simulations.

Investigation of phase stability and martensitic transformation of all-d-metal Heusler alloys Fe2VIr and Fe2TaIr in high pressure: A first-principles study

First-principles calculations are used to investigate the phase stability and martensitic transformation of two new all-d-metal Heusler alloys Fe2VIr and Fe2TaIr at 0–50 GPa. The difference in phase stability between Fe2VIr and Fe2TaIr is due to the effect of d-d orbital hybridisation between different atoms and the appearance of triply degenerate in the pressure-induced phonon optical modes. The softening behaviour of the transverse phonon mode along the high symmetry point X is responsible for the martensitic transformation of Fe2TaIr. We also observed the softening of the shear elastic constant C′ = (C11-C12)/2. Strong Fe-Fe magnetic coupling, softening of transverse acoustic phonon modes and anomalous softening of C′ awaken the martensitic transformation. Low-frequency phonon hybridisation of the heavy elements Ta and Ir is the driving force behind the softening. A surprising phenomenon is found during tetragonal deformation of the structure of Fe2TaIr at 45 GPa, whereby the structure break through the energy barrier of the leap and produced a tetragonal martensitic phase with a much lower energy. It may imply that pressure-induced Fe2TaIr produced a premartensitic phase. This work presents a detailed analysis of the anomalous softening behaviour of Fe2TaIr and the mechanism of the pressure-induced martensitic transformation. A new idea is proposed for an in-depth study of the martensitic phase transition precursor reaction.

The mode detangler.

Astrophotonics aims to transfer photonic technology to the development of compact astronomical instruments. However, light coupling from a multimode fiber, typically adopted in modern observatories, to a single-mode photonic device still poses a challenge. Though a photonic lantern can enable this transition in a low-loss way, it requires that the number of single-mode fibers (SMFs) at the output is the same as the number of guided modes in the multimode fiber, resulting in a cumbersome fan-out of many single-mode devices to be connected. Herein, we invent an active device in a waveguide form called "the mode detangler" (MD). We show that it can adaptively transform a complex light field from a multimode fiber to a single-mode-like spot. In this way, only one single-mode device is required at the end. The path leading to the idea and the theory behind the mode detangling effect is explained, followed by numerical simulations and experimental demonstrations using a few-mode fiber as proof of concept. We believe this device has the potential to address the multimode-to-single-mode conversion challenge in astrophotonics but also sheds light on (de)multiplexing applications regarding spatial mode technology in optical communications.

Synthesis and study of nonlinear optical properties of an enaminone derived from dibenzoylmethane and N,N-diethylaminoaniline

The compound, (Z)-3-((4-(diethylamino)phenyl)amino)-1,3-diphenylprop-2-en-1-one, is synthesized by the reaction of dibenzoylmethane and 4-N,N-diethylaniline. The relative stabilities of the possible tautomers of the molecule are studied via the DFT B3LYP-D3BJ, CAM-B3LYP, M062X, and ωB97XD functionals in conjunction with the 6-311++G(d,p) basis set. The results showed that the enaminone tautomer with the intramolecularly hydrogen bonded chelated ring is the most stable. This is further confirmed by the Car–Parrinello MD calculations in the gas phase as well as the NCI analysis. The electronic spectrum is calculated by the TD DFT B3LYP/c-pVDZ level in ethanol, and the hole–electron analysis is carried out for the interpretation of the bands, which revealed that the longest one at 430 nm is of charge transfer origin while the others are of local transition origin. Atoms-in-molecules calculations in several media and levels of theory predicted that the ρBCP at the hydrogen bond in the gas phase to be 0.03791–0.04255 e/a0 3 which is a characteristic of a medium strong hydrogen bond. Researchers investigated the enaminone’s nonlinear optical (NLO) characteristics when it was exposed to a low power (<1 Watt), single fundamental transverse mode laser beam at 473 nm. By using diffraction patterns (DPs) and Z-scan methods, we calculated the nonlinear refractive index (NLRI) of the enaminone up to 4.597 × 10−11 m2 W−1 using DPs. The resulting DPs are numerically investigated using the Fraunhofer (F.) approximation and the Fresnel-Kirchhoff (F.K.) diffraction integral, showing excellent agreement with experimental findings. We successfully explored all-optical switching (AOS) in enaminone using two laser beams.

Reliability analysis of output electrical response performance of multi-state flexoelectric structures under single and multiple failure modes

This paper proposes a reliability model of flexoelectric beams in the electrical open and short circuit states when different failure modes and the multiple failure modes of the output electrical response performances are considered, respectively. The reliability indices of the flexoelectric beams in the two circuit states can be defined based on the output electrical response models. Sequentially, the importance sampling (IS) and the mixed importance sampling (IS) methods are respectively used to calculate the reliability of the flexoelectric beams in single and multiple failure modes. The reliability results of the flexoelectric beams are verified by comparing them with the results of the Monte Carlo Simulation (MCS). The numerical results show that the flexoelectric beam is entered into a relatively safe and reliable state when the critical value of the open circuit voltage of 0.235 V and the thickness of the flexoelectric beams of 1 mm are considered as well as the length-thickness ratio of 20.

The optical properties of nano-structural α-Fe2O3 dependence on the shape.

Three different crystal morphologies of α-Fe2O3, including uniform hexagonal, square, and rhombic shapes, were prepared according to the aqueous-thermal reaction. The hexagonal-shaped α-Fe2O3 was enclosed by the 104 plane, while the square and rhombic structures were enclosed by the 110 plane. Two absorption peaks at 455 and 532 cm-1 were found for the perpendicular (⊥) modes, and one absorption peak at 650 cm-1 appeared for the parallel (||) mode for hexagon-shaped α-Fe2O3 during analysis by Fourier-transform infrared spectroscopy. However, the peaks of square- and rhombic-shaped α-Fe2O3 for perpendicular (⊥) mode blueshifted, and the former two peaks merged together forming a broad band at approximately 480 cm-1. For Raman spectra determination, the peaks arose from the Brillouin zone center, and two additional peaks were observed at 660 and 1320 cm-1, belonging to 1 longitudinal optical (1LO) and 2 longitudinal optical (2LO) modes. All three materials exhibited higher intensities when excited at a wavelength of 633 cm-1. Furthermore, in the polarization state, the centers of all peak positions slightly shifted for hexagon-shaped α-Fe2O3, but all peak positions for square-shaped and rhombic-shaped α-Fe2O3 exhibited a significant blueshift. The structure of hexagon-shaped α-Fe2O3 was relatively tolerant regarding the polarization properties of vibration modes; however, the symmetry of crystal square-shaped and rhombic-shaped α-Fe2O3 changed, subsequently revealing different optical properties. RESEARCH HIGHLIGHTS: The hexagon-shaped, square-shaped, and rhombic-shaped α-Fe2O3 enclosed by different planes were synthesized. The Fourier Transform Infrared spectrometer peaks of α-Fe2O3 depended on their hexagon, square and rhombic shapes. Compared with hexagon-shaped α-Fe2O3, the Raman peaks for square and rhombi ones significantly shifted. The hexagon-shaped α-Fe2O3 is relatively tolerant regarding the polarization properties.

Comparison of Moses laser and Raykeen laser in patients with impacted upper ureteral stone undergoing flexible ureteroscopic holmium laser lithotripsy

BackgroundTo compare the operative effect and clinical efficacy of the Moses laser mode and the Raykeen holmium laser energy platform powder mode under flexible ureteroscopic lithotripsy in patients with impacted upper ureteral stones.MethodsFrom March 2022 to September 2022, 72 patients were divided into a Moses laser group and a Raykeen laser group according to surgical method, with 36 patients in each group. CT and ureteroscopy confirmed that all patients had isolated impacted upper ureteral stones. The stone volume (mm3), stone density (Hu) and severity of hydronephrosis were measured by CT. Postoperative complications were evaluated using the Clavien–Dindo score.ResultsThere were no complications of ureteral stenosis related to the laser treatment. The operative time and lithotripsy time were lower in the Moses laser group than in the Raykeen laser group (P < 0.05). The stone-free survival rate did not differ significantly between the two groups (P = 0.722). Stone volume was found to be positively correlated with laser energy and lithotripsy time in both groups (P < 0.01). There was no significant correlation between laser energy and lithotripsy time or ureteral stone density (Hu) in the Moses laser group (P > 0.05) or the Raykeen laser group (P > 0.05).ConclusionsThe contact mode of Moses technology and the powder mode of Raykeen laser lithotripsy can be used for the ablation of a single impacted upper ureteral stone. The ablation speed was related to the stone volume and the severity of polyp hyperplasia, not the stone density. We recommend the use of the powdered mode as a therapeutic measure for the treatment of impacted upper ureteral stones in flexible ureteroscopic lithotripsy.

Random Lasing under Dissipative Tunneling Conditions in a Network Quantum Material

A new mechanism of the generation of a random laser based on a random photonic network with dissipative tunneling of photons between microcavities that are placed at the nodes of such network and contain identical two-level quantum systems has been revealed. It has been shown that an additional source of photon losses in tunneling promotes the separation of individual modes of the random laser and the achievement of the lasing threshold even at a vanishingly small population inversion. In this case, the enhancement of laser modes has an interference nature and is due to the energy redistribution between the nodes of the photonic network that correspond to different signs of the frequency detuning of stationary modes of the random laser from the transition frequency of two-level systems. It has been shown that the traditional lasing mechanism, which demonstrates features of the spectrum of single microcavities, i.e., is almost independent of the topological properties of the network and the tunneling parameter, is present in the region of zero detuning.

Multipeak ultraviolet lasing based on F-P mode from in-situ ZnO nanowire

Abstract High-quality ultraviolet singlemode and multimode lasing from zinc oxide nanowires are highly desirable. In this paper, we achieve high-Q lasing oscillation in vertically grown Zinc oxide (ZnO) microwires. The broad gain range reaches 13 lasing modes under high-energy excitation. We observe multiple peak emissions from the Fabry-Perot (F-P) lasing mode. In contrast, nanorod arrays with low aspect ratios exhibit amplified spontaneous emission (ASE) due to significant diffraction losses. Our work demonstrates that high-quality ZnO nanowires with an appropriate aspect ratio realize high-Q ultraviolet multipeak lasing based on F-P mode. These findings will benefit the design and fabrication of nanolasers based on nanowires.

Unsupervised Deep Tensor Network for Hyperspectral-Multispectral Image Fusion.

Fusing low-resolution (LR) hyperspectral images (HSIs) with high-resolution (HR) multispectral images (MSIs) is a significant technology to enhance the resolution of HSIs. Despite the encouraging results from deep learning (DL) in HSI-MSI fusion, there are still some issues. First, the HSI is a multidimensional signal, and the representability of current DL networks for multidimensional features has not been thoroughly investigated. Second, most DL HSI-MSI fusion networks need HR HSI ground truth for training, but it is often unavailable in reality. In this study, we integrate tensor theory with DL and propose an unsupervised deep tensor network (UDTN) for HSI-MSI fusion. We first propose a tensor filtering layer prototype and further build a coupled tensor filtering module. It jointly represents the LR HSI and HR MSI as several features revealing the principal components of spectral and spatial modes and a sharing code tensor describing the interaction among different modes. Specifically, the features on different modes are represented by the learnable filters of tensor filtering layers, the sharing code tensor is learned by a projection module, in which a co-attention is proposed to encode the LR HSI and HR MSI and then project them onto the sharing code tensor. The coupled tensor filtering module and projection module are jointly trained from the LR HSI and HR MSI in an unsupervised and end-to-end way. The latent HR HSI is inferred with the sharing code tensor, the features on spatial modes of HR MSIs, and the spectral mode of LR HSIs. Experiments on simulated and real remote-sensing datasets demonstrate the effectiveness of the proposed method.

True random number generation based on temporal fluctuations of abalone shell coherent random lasers.

The output modes of random lasers exhibit randomness, making them a potential high-quality physical entropy source for generating random numbers. In this paper, we controlled a low-cost and easily fabricated abalone shell random laser, generating forward and backward coherent random lasers simultaneously in a single channel, resulting in highly diverse mode variations. After post-processing steps such as third-order difference calculations and exclusive-or (XOR) logic operations, we generated a random number sequence for the first time, to the best of our knowledge, based on the temporal fluctuations of biomimetic random laser coherent modes. The instantaneous generation rate reached a preliminary 40 Gbps. Moreover, the random bits satisfy requirements such as random distribution, independence, and absence of bias, successfully passing the NIST SP800-22 standard test, confirming the high quality of the random number sequence.

49650 Topical application of indocyanine green and 785 nm picosecond laser with diffractive optical element mode for skin rejuvenation in Asians

49650 Topical application of indocyanine green and 785 nm picosecond laser with diffractive optical element mode for skin rejuvenation in Asians

Fabrication of microchannels on silica glass by femtosecond laser multi-scan: From surface generation mechanism to morphology control

Femtosecond laser processing has become a critical technique for the microfabrication of hard and brittle materials, particularly in microfluidic device applications. This study focuses on the fabrication of microchannels with controllable cross-sectional profiles in silica glass, a material known for its excellent physical and chemical properties. Through a combination of experimental research and theoretical analysis, the surface generation mechanisms governing microchannel morphology are investigated, alongside the influence of various processing parameters on the surface roughness at the microchannel bottom. A comprehensive optimization method is developed to control sidewall taper and surface roughness by adjusting laser scanning paths and modes. Utilizing a composite scanning approach, the study achieves near-rectangular microchannels with average sidewall taper angles below 5° and surface roughness (Sa) of 2.53 μm. These results provide a new strategy for precise control of microchannel morphology in silica glass, offering significant potential to enhance the efficiency and precision of microfluidic device fabrication, with broad applications in both industrial and research settings.