Beam Propagation Research Articles

Switchable anisotropic diffraction mode filter based on fork-like liquid crystal gratings

The interaction of liquid crystal (LC) fork-like gratings (FLGs) with a Laguerre–Gaussian beam of the TEM00 mode is described. It is experimentally shown that when the direction of the light polarization vector differs from the direction of the LC eigenvectors, the medium behaves as an FLG with a controlled modulation depth, and in the opposite case, it is isotropic and homogeneous. Distributions of the intensities of the longitudinal section of the beam in the infinitely far field are given depending on the FLG rotation angle in the plane perpendicular to the direction of beam propagation. It is shown that the LC FLG functions as a switchable anisotropic diffraction mode filter.

Coherent propagation of high-power wave beams in hollow gas-filled daisy-shaped waveguides

Coherent propagation of high-power wave beams in hollow gas-filled daisy-shaped waveguides

Distortion-Corrected Posterior Ocular Shape in Myopic Eyes Assessed by Ultrawide OCT Detects Deformations Associated With Vision-Threatening Changes.

To develop a quantitative tool for assessing the posterior ocular shape using widefield, volumetric optical coherence tomography (OCT) in eyes with myopia. This observational, cross-sectional study included 178 eyes from 113 participants. Participants underwent a standardized eye examination, including ocular biometry and a custom ultrawide OCT. True ocular shape was reconstructed by tracing the beam propagation from the system to the posterior eye. Gaussian curvature quantified the localized ocular shape, which was further categorized into five distinct categories. An ocular shape irregularity (OSI) was calculated using principal component analysis. Linear regression with breakpoints analyzed the relationship between ocular shape parameters and axial length (AL). Increased curvature mean and variance were associated with more severe myopia (P < 0.001). Curvature categories (convex, normal, concave, and highly concave) differed significantly between the groups (all P < 0.001). Their correlations with AL revealed significant breakpoints between 27.1 and 27.2 mm. OSI, as a single metric for quantifying ocular shape distortion, was associated with more severe myopia (P < 0.001), and its correlation with AL revealed a breakpoint at 27.2 mm with a fourfold increase in slope steepness beyond this pivot. Determination of OSI was highly reproducible and could also be obtained with fewer scans. Eyes exceeding 27.2 mm in length exhibit pronounced shape changes. Our framework can be seamlessly integrated into commercial OCTs for ocular shape deformation detection, which could aid in identifying eyes with pathologic myopia.

Design and implementation of broadband optical vortices in photonic crystal slabs

We propose and discuss a simple method to generate broadband optical vortices, utilizing the inherent topological vortex structures of polarization around bound states in the continuum supported by a photonic crystal slab in the momentum space to induce the generation of vortex beams. Since the proposed structure is composed of silicon pillars arranged periodically, it lacks a true optical geometric center. It is insensitive to the position of the incident light and does not require a specific optical alignment process compared to traditional spiral phase plates. Furthermore, because it is composed of dielectric pillars, it can achieve vortex beam generation at any desired working wavelength. We also discuss the robustness of its structure, showing that it can be immune to certain manufacturing defects. Therefore, the proposed structure not only provides a new method for manipulating the angular momentum of photons but also has potential new applications in integrated optical information processing and optical tweezers.

Phase-modulated Airy beam generation by a leaky-wave structure

Phase-modulated Airy beam generation by a leaky-wave structure

Generation of the flat-top beam using convolutional neural networks and Gerchberg-Saxton algorithm

Abstract Laser technology has made rapid progress in recent years and has been widely used in various fields such as medicine, biology, military, and materials science. However, the limitations of traditional Gaussian intensity distribution of the laser beams in applications have prompted the emergence and development of flat-top beam shaping technology, which has received widespread attention. Here, we introduce a new method for generating flat-top beams that combines the traditional Gerchberg-Saxton algorithm with convolutional neural networks, using spatial light modulators to achieve flat-top beam shaping. A comparative analysis was conducted by comparing the root mean square error and diffraction efficiency of the generated flat-top beam with the results obtained using only the traditional Gerchberg-Saxton algorithm. Compared with the traditional Gerchberg-Saxton algorithm, the method proposed in this paper can generate a flat-top beam with smaller differences from the target light intensity and higher energy utilization, providing new possibilities for the application of laser technology.

Generation of switchable rectangular pulsed cylindrical vector beams in a 1.7 µm mode-locking all-fiber laser

In this paper, we demonstrate the generation of switchable rectangular pulsed cylindrical vector beams in a 1.7 µm mode-locking all-fiber laser by nonlinear amplifying loop mirror for the first time. Based on the nonlinear amplifying loop mirror mode-locking technology and mode selection coupler, the rectangular pulsed CVBs can be achieved and switched repeatedly and easily between the dissipative soliton resonance and noise-like pulse states. Furthermore, with the increasing of pump power, the duration of dissipative soliton resonance and noise-like pulse increase from 1.76 ns to 6.36 ns and 1.15 ns to 3.95 ns, respectively. In the meanwhile, both the peak power of dissipative soliton resonance and noise-like pulse are all clamped at 6 W all the time, showing the independence of clamped peak power and pulse type. Our work not only broadens wavelength range of switchable rectangular pulse, but also provides a novel pulse profile application of cylindrical vector beams.

Multiring polygon super-geometric beam generation based on quasi-frequency- degeneracy state of multiaxial super- geometric mode laser

Multiring polygon super-geometric beam generation based on quasi-frequency- degeneracy state of multiaxial super- geometric mode laser

Polarization Volume Hologram for On‐Chip Wavefront Engineering

AbstractLiquid crystal (LC) planar optics have advanced wavefront engineering toward ultrathin designs, capturing widespread attention. However, most wavefront control in LC planar optics remains constrained to freespace due to limitations in the precision of freely controllable units. Here, LC on‐chip wavefront engineering is proposed and confirmed. By controlling the initial azimuth angle of the polarization grating, the initial phase can be engineered, as theoretically predicted by rigorous coupled‐wave analysis. Experimentally, the initial azimuth angle of a polarization volume hologram grating, used as a waveguide coupler, is ingeniously modulated using a holographic template. Consequently, several on‐chip optical elements, including lenses, vortex beam generators, and holograms, are demonstrated. Furthermore, exit pupil expansion and multiexposure technologies are adopted to enhance off‐chip functionality and enable multifunctional, highly integrated LC on‐chip photonic systems. The proposed LC on‐chip wavefront engineering may find applications in freeform optics, near‐eye displays, LIDAR, and integrated photonic systems.

Topology-optimized terahertz real-time reconfigurable multifunctional liquid-crystal-coding metasurface

In this paper, a reflective terahertz reconfigurable multifunctional coding metasurface based on topology optimization using liquid crystal (LC) is presented. First, the LC metasurface unit is topologically optimized using the NSGA-II multi-objective optimization algorithm. By applying the bias voltage to dynamically adjust the dielectric constant of the LC, the metasurface unit is capable of 2-bit coding at the frequency of 0.67 THz. Then, based on the designed metasurface unit, the array arrangements of the coding metasurface are reversely designed, which makes the metasurface realize flexible control and dynamic switching between beam assignment and vortex beam generation. The results show that for the beam assignment, the single-beam and multi-beam control can be realized with the reflected electromagnetic waves at continuous arbitrary angles in the range of elevation angle of 40° and azimuth angle of 360°. Moreover, the elevation angle and azimuth angle of each beam in the multi-beam can be controlled independently. Using the Fourier convolution addition operation, the control range of the single-beam elevation angle can be expanded. For the vortex beam, the single vortex beam and the multi-vortex beam can be generated in the range of elevation angle of 40° and azimuth angle of 360° with topological charges l=±1, ±2, ±3 at arbitrary angles. This provides flexibility and diversity in the generation of vortex beams. Therefore, the proposed terahertz LC metasurface can realize flexible control of reconfigurable functions and has certain application prospects in terahertz communication, phased array radar, and vortex radar.

3D-printed OAM beam generator with enhanced out-of-band gain filtering characteristic

3D-printed OAM beam generator with enhanced out-of-band gain filtering characteristic

Second Harmonic Generation of High Power Cosh-Gaussian Beam in Thermal Quantum Plasma: Effect of Relativistic and Ponderomotive Nonlinearity

Second harmonic generation (SHG) of high power Cosh-Gaussian(ChG) beam in thermal quantum plasma (TQP) is explored in current investigation. Relativistic and ponderomotive nonlinearities are taken together in present investigation. Combination of relativistic-ponderomotive nonlinearities causes modification in electron mass, thereby producing density gradients inside plasma. This further produces self-focusing of main beam. The well-known WKB and paraxial approaches are used for solving main beam’s wave equation and to obtain 2nd order ordinary differential equation (ODE). There is generation of electron plasma wave (EPW) due to these density gradients. Excited EPW interacts with main beam to generate 2nd harmonics in plasma. Effects of combined relativistic-ponderomotive nonlinearities and established laser - plasma parameters on beam’s waist and SHG yield are studied in present study.

Generation of pseudo-nondiffracting symmetrical Layer beams using cylindrical lenses

The pseudo-nondiffracting behavior of optical caustic beams makes them potentially useful in precise component alignment at CERN. This paper introduces an innovative method for generating one and two-dimensional symmetrical Airy-like beams, known as Layer beams, utilizing a specific configuration of plano-convex cylindrical lenses. Simulations and experimental results have validated this method, demonstrating its potential for scalable and cost-effective beam production with tunable properties, making it practical for a wide range of scientific applications.

Twisted Metasurfaces for On‐Demand Focusing Localization

AbstractDynamic focusing of electromagnetic (EM) waves is a cornerstone in various applications, encompassing aerospace communication, sensing, and high‐resolution imaging. Recently, the advent of intelligent metasurfaces, hailed as the next evolutionary step, has revolutionized self‐adaptive functionalities. However, their extensive embeddings of active components pose a great challenge associated with escalated costs, heightened power consumption, and increased complexity, thus hindering large‐scale implementation. Here, a cost‐effective approach for dynamic EM focusing utilizing a twisted metasurface is introduced, which integrates a transmissive layer with a reflective layer in a cascade fashion. This innovative design leverages the mutual rotation between two layers to enable the precise manipulation of beam propagation and scanning area, allowing for the flexible localization of the focal point across a wide range, spanning −44.17° to 44.17° in elevation and 0° to 360° in azimuth. This capability is underpinned by the strategic fusion of multiple phase profiles, including gradient and Gaussian phase. In the experiment, a goal‐oriented system is built up whose outcomes demonstrate a striking alignment with the simulated results, achieving a correlation coefficient of 96.7%. This work presents a streamlined pathway toward dynamic EM focusing and the related applications constrained by space and power limitations.

Composite underwater optical wireless channel modeling based on the electric field Monte Carlo method

In this study, we propose a simulation method to investigate the scattering characteristics of beams with specific phase structures in waters containing micrometer-scale particles and bubbles. This method is based on the electric field Monte Carlo (EMC) algorithm and utilizes the Mie theory and ray tracing method. We simulate the propagation of orbital angular momentum (OAM) beams in a composite underwater channel using the proposed method and analyze the impact of bubble density on the spiral phase distribution of the OAM beams. We also design an underwater experiment in a water tank to simulate the propagation of OAM beams in the composite channel. The results reveal that the power of the desired mode of the OAM beam decreases as the bubble density increases, which is consistent with the simulation results. This method facilitates a realistic simulation of structured light beam propagation in waters containing particles and bubbles and can provide reference data for studying the scattering characteristics of structured beams in composite underwater channels.

Multiplicity of solutions for a nonhomogeneous quasilinear elliptic equation with concave-convex nonlinearities

Abstract We investigate the multiplicity of solutions for a quasilinear scalar field equation with a nonhomogeneous differential operator defined by S u ≔ − div ϕ u 2 + ∣ ∇ u ∣ 2 2 ∇ u + ϕ u 2 + ∣ ∇ u ∣ 2 2 u , Su:= -\hspace{0.1em}\text{div}\hspace{0.1em}\left\{\phi \left(\frac{{u}^{2}+{| \nabla u| }^{2}}{2}\right)\nabla u\right\}+\phi \left(\frac{{u}^{2}+{| \nabla u| }^{2}}{2}\right)u, where ϕ : [ 0 , + ∞ ) → R \phi :\left[0,+\infty )\to {\mathbb{R}} is a positive continuous function. This operator is introduced by Stuart [Two positive solutions of a quasilinear elliptic Dirichlet problem, Milan J. Math. 79 (2011), 327–341] and depends on not only ∇ u \nabla u but also u u . This particular quasilinear term generally appears in the study of nonlinear optics model, which describes the propagation of self-trapped beam in a cylindrical optical fiber made from a self-focusing dielectric material. When the reaction term is concave-convex nonlinearities, by using the Nehari manifold and doing a fine analysis associated on the fibering map, we obtain that the equation admits at least one positive energy solution and negative energy solution, which is also the ground state solution of the equation. We overcome two main difficulties which are caused by the nonhomogeneity of the differential operator S S : (i) the almost everywhere convergence of the gradient for the minimizing sequence { u n } \left\{{u}_{n}\right\} ; (ii) seeking the reasonable restrictions about S S .

Highly Efficient and Integrated Nonlinear Airy Beams Generation

AbstractOwing to its peculiar non‐diffraction, self‐acceleration, and self‐healing properties, the Airy beam has attracted a great deal of attention in various fields such as micro‐manipulation, plasma generation, and optical microscopy. To date, it is still a challenge to generate nonlinear Airy beams with microstructure efficiently, thus limiting applications of such Airy beams. Here, a novel and efficient method for generating Airy beams is experimentally demonstrated by microstructure on a nonlinear crystal surface, which is fabricated by a focused ion beam (FIB) technique. The second‐harmonic (SH) Airy beams are generated in the far field and characterize their intensity distributions, which agree well with theoretical results. Then, the self‐accelerating and self‐healing properties of the generated SH Airy beams are demonstrated. Besides, the normalized efficiency of SH Airy beams is measured at (1.44 × 10−5%W−1), and compare the efficiency of different methods of generating nonlinear Airy beams, which shows the advantages of this method. The proposed method of generating nonlinear Airy beams shows great potential for integrated optics, optical micro‐machining, and advanced imaging.

High energy circular Pearcey beams generation using phase-only metasurfaces with complex function fitting method

In this paper, we use electromagnetic metasurfaces for the first time to generate the circular Pearcey beam. A complex function fitting method is proposed for generating the circular Pearcey beam, which can improve electric field intensity at focusing location, resulting in a high energy circular Pearcey beam with an increase of 31.77% compared to the traditional Pearcey beam design. A slowly varying envelope is applied to describe the amplitude of the Pearcey function. Meanwhile, considering the oscillation property of the Pearcey function, an additional phase is added to its original phase. Furthermore, the double-phase hologram (DPH) method is developed to realize phase-only metasurface design. Four full wave electromagnetic simulations are finished, which prove the effectiveness of our proposed Pearcey function fitting method and phase-only metasurface design. Two 10 GHz transmissive metasurfaces were designed, fabricated, and experimented to further validate our design. This circular Pearcey beam design is useful in near field wireless communication, microwave wireless power transmission, and simultaneous wireless information and power transfer.

Propagation of Sine hyperbolic Gaussian vortex beam (ShGvB) in vertical anisotropic oceanic turbulence with adaptive optics correction

The propagation of Sinh Gaussian vortex beam (ShGvB) along vertical anisotropic oceanic turbulence is established using the spatial power spectrum which depends upon the depth of the ocean. The average intensity of the beams has been derived. For 100 m depth, the average intensity has been plotted and studied using the measured salinity and temperature from the ocean in both isotropic and anisotropic oceanic turbulence systems. The average transmittance of the ShGvB is studied and found that the beam degrades faster in anisotropic media than in isotropic media. To mitigate the aberrations adaptive optics (AO) correction is incorporated in the study along the vertical link. Quantitative estimates of the Bit error rate (BER) have been made to evaluate the beam's performance for vertical underwater optical communication and found that by improving the signal-to-noise ratio and incorporating AO, the ShGvB performs effectively in vertical underwater optical communication.

Compact multi-ring perfect vortex beam generator fabricated by laser direct writing

Perfect vortex beams (PVBs) have received much attention in recent years since the annular intensity distributions are independent of the topological charge (TC). However, the cost-effective preparation of micrometer-scale monolithic devices capable of generating multiple PVBs through a simple approach remains a significant challenge. In this work, a design of double-ring perfect spiral phase plates (DPSPPs) is presented for the generation of PVBs at two distinct locations along the radial direction. The respective radii and spacing of the double-ring PVBs can be tuned by changing the control parameters. The proposed DPSPPs are fabricated by the flexible femtosecond laser direct writing (FsDLW) technique. The experimentally generated double-ring vortex beams with different TCs possess an almost constant radius, which is consistent with the characteristics of PVBs. Furthermore, the double-ring PVBs with different fractional and trigonometric function TCs and the multi-ring PVB are also demonstrated. The design and fabrication methods are expected to facilitate the miniaturization of the applications of PVBs in optical manipulation, optical communication, and high-capacity information storage.