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Phase-structured light beams carrying orbital angular momentum (OAM) have a wide range of applications ranging from particle trapping to optical communication. Many techniques exist to generate and manipulate such beams but most suffer from bulky configurations. In contrast, silicon photonics enables the integration of various functional components on a monolithic platform, providing a way to miniaturize optical systems to chip level. Here, we propose a series of on-chip subwavelength holographic waveguide structures that can convert the in-plane guided modes into desired wavefronts and realize complex free-space functions, including the generation of complex phase-structured light beams, arbitrarily directed vortex beam emission and vortex beam focusing. We use a holographic approach to design subwavelength holographic surface gratings, and demonstrate broadband generation of Laguerre–Gaussian (LG) and linearly polarized (LP) modes. Moreover, by assigning appropriate geometric phase profiles to the spiral phase distribution, the off-chip vortex beam manipulation including arbitrarily directed emission and beam focusing scenarios can be realized. In the experiment, directed vortex beam emission is realized by using a fabricated tilt subwavelength holographic fork grating. The proposed waveguide structures enrich the functionalities of dielectric meta-waveguide structures, which can find potential applications in optical communication, optical trapping, nonlinear interaction and imaging.

The longitudinal distributions of the maximum intensity in Bessel light beams (BLBs) of various orders are compared with analogous distributions in Gaussian and Laguerre-Gaussian light beams of the corresponding orders. The concept of a “dangerous zone” of the BLB is introduced. A method for determining its length is proposed. The maximum intensity I 0 of the initial Gaussian or Laguerre-Gaussian light beam is initially chosen not to exceed the optical damage threshold of the optical elements and objects used. The dangerous zone of the BLB is the region of space behind the axicon in which the maximum intensity in the BLB exceeds I 0 . The length of the dangerous zone is taken to be the largest distance z K behind the axicon for which the maximum intensity in the BLB cross section is equal to I 0 . Additionally, the distance z E from the axicon at which the intensity on the BLB axis and in its peripheral annular field are aligned is determined. The maximum intensity in this cross section in BLBs of the 0th, 1st, and 2nd orders are guaranteed to be less than I 0 although the transverse size of the light beam is not yet too large. The relative (in units of the BLB existence length z wI ) values of z E and z K for the zero and higher (from the 1st to the 9th) orders of the BLB are calculated with the help of mathematical modeling methods. It is advisable to place objects with low optical damage thresholds at distances greater than z K when designing optical systems using the conical BLB geometry. The 1st order BLB in the region from z K to z E is the most energy efficient for the same given radius of the initial Laguerre-Gaussian beam in terms of the level I 0 / e 2 .

Structured light beams have recently attracted enormous research interest for their unique properties and potential applications in optical communications, imaging, sensing, etc. Since most of these applications involve the propagation of structured light beams, which is accompanied by the phenomenon of diffraction, it is very necessary to employ diffraction theories to analyze the obstacle effects on structured light beams during propagation. The aim of this work is to provide a systematic summary and comparison of the scalar diffraction theories for structured light beams. We first present the scalar fields of typical structured light beams in the source plane, including the fundamental Gaussian beams, higher-order Hermite–Gaussian beams, Laguerre–Gaussian vortex beams, non-diffracting Bessel beams, and self-accelerating Airy beams. Then, we summarize and compare the main scalar diffraction theories of structured light beams, including the Fresnel diffraction integral, Collins formula, angular spectrum representation, and Rayleigh–Sommerfeld diffraction integral. Finally, based on these theories, we derive in detail the analytical propagation expressions of typical structured light beams under different conditions. In addition, the propagation of typical structured light beams is simulated. We hope this work can be helpful for the efficient study of the propagation of structured light beams.

The influence of three factors on the formation of a Bessel light beam (BLB) in the scheme of transforming a Gaussian beam by an axicon were investigated using Fourier optics via numerical simulation. The factors were the ellipticity of the incident light beam, the ellipticity of the axicon, and the presence of a round tip on the axicon. The results of the influence of each factor on the structure and quality parameters k c , k r , and ⟨R 2 ⟩. of the formed BLB and its Fourier spectrum (FSBLB) are shown. The quality parameters of the FSBLB k Is , k ws , and k rs , which characterized the spread of the amplitude, half-width, and average frequency of the conical component of the FSBLB, and the parameter η, which determined the ratio of the energy in the conical component to the total energy of the beam, were introduced to analyze the quality of the FSBLB. The ellipticity of the Gaussian beam incident on the axicon led to a reduction in the length of the BLB region of existence. However, all quality parameters decreased, with the coefficient of constancy k c dropping most quickly, as the longitudinal coordinate increased. FSBLB quality parameters k Is and k ws , which characterized the spread of the intensity and half-width of the conical component of the beam, decreased with increasing eccentricity of the Gaussian beam half-width ε b . The ellipticity of the axicon affected all BLB quality parameters, most clearly the coefficient of constancy k c and the average value of R 2 , which decreased with an increase in the axicon eccentricity ε a . This happened because of oscillations in the ring closest to the BLB axis. The shape of the FSBLB also changed with increasing ε a , transitioning from circular to elliptical and causing the coefficient of constancy of the conical component spectral frequency to decrease. Regularities in the transverse intensity distributions of BLBs formed by azimuthal modulation of the cone angle were considered for the case where the number N of complete oscillation periods of the cone angle were >2. The number of intensity minima in the paraxial ring for a small axicon base angle modulation amplitude B (≤ 0.05) was equal to N for odd N and equal to 2N for even N. The number of minima in the paraxial ring of the beam was equal to 2N for large B values (>0.05) for both even and odd N. A spherical tip of an otherwise conical axicon led to the formation of a separate non-conical component in the spectrum. A hyperbolic axicon broadened the conical component of the spectrum in the direction of low spatial frequencies. The results could be used to form special light fields and to assess the quality of manufactured axicons and the ellipticity of a beam incident on an axicon.

As one key candidate technology for the 6G internet of vehicles, vehicular visible light communications (VLCs) have received widespread attention and discussion due to their inherent advantages, including broadband, green, security, and ubiquity. In order to improve the quality of vehicular VLC links and extend their coverage, various multiple input multiple output (MIMO) techniques have been actively introduced into the field of vehicular VLC, demonstrating the corresponding performance gain potential. Objectively, the existing research works mentioned above are generally limited to the discussion of MIMO vehicular VLC based on conventional Lambertian light-emitting diode (LED) light sources. Consequently, there is one absence of a targeted study and evaluation of the link configuration-based vehicular non-Lambertian LEDs and the potential non-Lambertian MIMO vehicular VLC. To address the limitations of the aforementioned research and explore the novel spatial dimension for vehicular VLC design, this work attempts to introduce the representative non-Lambertian LED light beams into the typical MIMO vehicular VLC application for constructing novel MIMO vehicular VLC transmission links. The numerical results demonstrate that in 2 × 2 MIMO mode, compared to the benchmark Lambertian vehicular VLC scheme, the proposed typical non-Lambertian NSPW vehicular VLC schemes could provide capacity gains of up to 5.18 bps/Hz and 4.71 bps/Hz for the stop mode, and the traffic mode, respectively. Moreover, this article quantitatively evaluates the impact of the spatial spacing of receiver light beams on the performance of MIMO vehicular VLC and the relevant fundamental characteristics.

Structured light beams have played important roles in the fields of optical imaging and optical manipulation. However, light fields scatter when they encounter highly anisotropic scattering media, such as biological tissue, which destroys their original structured fields and turns them into speckle fields. To reconstruct structured light beams through highly anisotropic scattering media, we present a method based on intensity transmission matrix which only relates the input and output light intensity distributions. Compared with the conventional method which relies on the measurement of complex-valued transmission matrix, our scheme is easy to implement, fast and stable. With the assistance of spatial filters, three kinds of structured light beams, Bessel-like beams, vortex beams and cylindrical vector beams, were constructed experimentally through a ZnO scattering layer. The present method is expected to promote optical applications through highly anisotropic scattering media.

The interaction of a Gaussian vortex beam (GVB) with metamaterials during its propagation is of significant interest to the optical community. These GVBs are classified as structured light beams that possess orbital angular momentum (OAM). Understanding the behavior of structured light beams is essential for clarifying fundamental interaction mechanisms with metamaterial structures. So, this work delves into the investigation of the propagation characteristics of a GVB within a chiral material. The analytical expressions for GVB propagating through a chiral medium are obtained by using the extended Huygens–Fresnel diffraction integral formula and the optical ABCD matrix system. In a chiral medium, GVB exhibits a tendency to fragment into a left circularly polarized (LCP) beam and a right circularly polarized (RCP) beam, each following its unique propagation paths. The beam intensity and gradient force are computed and discussed for OAM mode number, beam waist radius, and chirality parameter. This research will be quite helpful for light manipulation, optical sorting, optical radiation force, the radiative transfer process, and optical guiding.

We study the conditions for the formation and transformation of the Bessel plasmon-polariton field in a dielectric-metal structure excited by a Bessel light beam with arbitrary polarization. The effect of the metal layer thickness on the resulting plasmon field structure is investigated. The formation of Bessel plasmon-polaritons in a scheme consisting of a conical axicon with its base in contact with a silver layer of defined thickness is simulated.

The propagation and scattering of vortex light beams in complex media have significant implications in the fields of laser imaging, optical manipulation, and communication. This paper investigates the scattering characteristics of vortex light beams from a random rough surface. Firstly, a two-dimensional Gaussian rough surface is generated using the Monte Carlo method combined with the linear filtering method. Subsequently, the vortex beams are decomposed into the superposition of infinite plane waves, and the scattering of each plane wave from the rough surface is calculated using the Kirchhoff Approximation method. Numerical results of the angle distribution and spatial distribution of OAM scattering Laser Radar Cross Section (LRCS) are presented, varying with different surface roughness parameters for a rough aluminum surface and the beam’s parameters. The results demonstrate that the scattering of vortex beams is influenced by the beam’s parameters, such as Orbital Angular Momentum (OAM) mode number and elevation angle, which may bring new insights into vortex wave-matter interactions and their applications in high resolution imaging.