Structured Light Fields Research Articles

The Optical Forces and Torques Exerted by Airy Light-Sheet on Magnetic Particles Utilized for Targeted Drug Delivery

The remarkable properties of magnetic nanostructures have sparked considerable interest within the biomedical domain, owing to their potential for diverse applications. In targeted drug delivery systems, therapeutic molecules can be loaded onto magnetic nanocarriers and precisely guided and released within the body with the assistance of an externally applied magnetic field. However, conventional external magnetic fields generated by permanent magnets or electromagnets are limited by finite magnetic field gradients, shallow penetration depths, and low precision. The novel structured light field known as the Airy light-sheet possesses unique characteristics such as non-diffraction, self-healing, and self-acceleration, which can potentially overcome the limitations of traditional magnetic fields to some extent. While existing studies have primarily focused on the manipulation of dielectric particles by Airy light-sheet, comprehensive analyses exploring the intricate interplay between Airy light-sheet and magnetic nanostructures are currently lacking in the literature, with only preliminary theoretical discussions available. This study systematically explores the mechanical response of magnetic spherical particles under the influence of Airy light-sheet, including radiation forces and spin torques. Furthermore, we provide an in-depth analysis of the effects of particle size, permittivity, permeability, and incident light-sheet parameters on the mechanical effects. Our research findings not only offer new theoretical guidance and practical references for the application of magnetic nanoparticles in biomedicine but also provide valuable insights for the manipulation of other types of micro/nanoparticles using structured light fields.

Nonlinear geometric phase coded ferroelectric nematic fluids for nonlinear soft-matter photonics

Simultaneous manipulation of multiple degrees of freedom of light lies at the heart of photonics. Nonlinear wavefront shaping offers an exceptional way to achieve this goal by converting incident light into beams of new frequencies with spatially varied phase, amplitude, and angular momenta. Nevertheless, the reconfigurable control over structured light fields for advanced multimode nonlinear photonics remains a grand challenge. Here, we propose the concept of nonlinear geometric phase in an emerging ferroelectric nematic fluid, of which the second-order nonlinear susceptibility carries spin-dependent nonlinearity phase. A case study with photopatterned q-plates demonstrates the generation of second-harmonic optical vortices with spin-locked topological charges by using cascaded linear and nonlinear optical spin-orbit interactions. Furthermore, we present the dynamic tunability of second-harmonic structured light through temperature, electric field, and twisted elastic force. The proposed strategy opens new avenues for reconfigurable nonlinear photonics, with potential applications in optical communications, quantum computing, high-resolution imaging, etc.

Toroidal phase topologies within paraxial laser beams

Control of topologies in structured light fields with multi-degrees of freedom integrates fundamental optical physics and topological invariance. Beyond the simple phase vortex, three-dimensional (3D) topological singularities and related nonsingular textures have recently gained significant interest. Here, we experimentally demonstrate the creation of a family of toroidal phase topologies within paraxial laser beams. By employing single two-dimensional (2D) phase control, we generate propagating 3D topological textures, effectively embodying the topological configuration of a four-dimensional (4D) parameter space. The resulting light fields exhibit amplitude isosurfaces of toroidal vortices and hopfionic phase textures, both controlled by topological charges. The ability to prepare scalar phase textures of light offers new insights into the high-dimensional control of complex structured textures and may find significant applications in light-matter interactions, optical manipulation, and optical information encoding.

Low-sampling and noise-robust single-pixel imaging based on the untrained attention U-Net

The single-pixel imaging (SPI) technique illuminates the object through a series of structured light fields and detects the light intensity with a single-pixel detector (SPD). However, the detection process introduces a considerable amount of unavoidable white noise, which has a detrimental effect on the image quality and limits the applicability of SPI. In this paper, we combine the untrained attention U-Net with the SPI model to reduce noise and achieve high-quality imaging at low sampling rates. The untrained U-Net has the advantage of not requiring pre-training for better generalization. The attention mechanism can highlight the main features of the image, which greatly suppresses the noise and improves the imaging quality. Numerical simulations and experimental results demonstrate that the proposed method can effectively reduce different levels of Gaussian white noise. Furthermore, it can obtain better imaging quality than existing methods at a low sampling rate of less than 10%. This study will expand the application of SPI in complex noise environments.

Designed 3D Dumpling‐Shaped Femtosecond Laser Structured Light Field for Nanoscale Sensing

AbstractNanoscale optical sensing plays a crucial role in achieving high‐precision non‐contact distance and displacement measurements. As one of the promising alternatives, structured light can greatly simplify optical sensing systems. In this study, a novel optical phenomenon of a structured beam called the “Dumpling‐shaped Structured Light Field” (DSLF) is revealed, which forms during the focusing of cylindrical lens beams. The 3D DSLF comprises two mutually perpendicular primary and secondary foci, offering unique possibilities in micro/nano processing and sensing applications. A thorough investigation of the DSLF is conducted, revealing a correlation between the secondary foci and the phase status at the objective lens's entrance pupil. The propagation of DSLF under tight focus conditions has been verified and discussed through methods of femtosecond laser two‐photon polymerization and light field analysis. Finally, thanks to the unique 3D intensity distribution of 3D DSLF, the applicability of DSLF in high‐precision position and vibration sensing has been demonstrated. By detecting the horizontal and vertical dimensions of the reflected DSLF, position and vibration sensing is achieved with a Z‐direction accuracy of 10 nm (λ/80). This research contributes to understanding structured light, and offers practical applications in various fields, including micro/nano laser processing, optical imaging, sensing, etc.

On-axis complex-amplitude modulation for the generation of super-stable vector modes

We propose a technique to generate complex vector beams with high quality and stability. Our approach relies on the combination of complex amplitude modulation (CAM) and on-axis modulation, two techniques that seem incompatible at first glance. The first one produces scalar structured light fields in phase and amplitude with high accuracy, while the second one is preferred for generating vector beams of great stability although of reduced quality. Specifically, the idea behind our technique is to send the shaped light produced by CAM co-axially with the zeroth order, rather than diffracted to the first order, as it is commonly done. We first describe our technique, explaining the generation of the hologram and experimental setup to isolate the desired vector mode, and then present experimental results that corroborate our approach. We first address the quality of the generated beams using Stokes polarimetry to reconstruct their transverse polarisation distribution, and then compare their stability against the same mode produced using a Sagnac interferometric method. Our vector beams are of good quality and remarkably stable, two qualities that we expect will appeal to the community working with vector modes.

Spatiotemporal Airyprime complex-variable-function wave packets in a strongly nonlocal nonlinear medium.

A type of circular Airyprime function of complex-variable Gaussian vortex (AFCGV) wave packets in a strongly nonlocal nonlinear medium is introduced numerically, combining the properties of helicity states and abrupt autofocusing. We investigate the effects of the chirp factor, distribution parameter, and decay factor on the AFCGV wave packets in the strongly nonlocal nonlinear medium. Interestingly, by adjusting the distribution parameter, the AFCGV wave packets can exhibit stable rotational motions in various shapes, such as symmetric lobes and doughnuts. In addition, the Poynting vector and the gradient force of the AFCGV wave packets are also discussed. Our research not only explains the theoretical model for controlling AFCGV wave packets but also advances fundamental research on self-bending and autofocusing structured light fields.

Group Control of Photo-Responsive Colloidal Motors with a Structured Light Field

Using structured light to drive colloidal motors, due to its advantages of remote manipulation, energy tunability, programmability, and the controllability of spatiotemporal distribution, has been attracting much attention in the fields of targeted drug delivery, environmental control, chemical agent detection, and smart device design. Here, we focus on studying the group control of colloidal motors made from a photo-responsive organic polymer molecule NO-COP (N,O-Covalent organic polymer). These colloidal motors mainly respond to light intensity patterns. Considering its merits of fast refreshing speed, good programmability, and high-power threshold, we chose a digital micromirror device (DMD) to modulate the structured light field shining on the sample. It was found that under ultraviolet or green light modulation, such colloidal motors exhibit various group behaviors including group spreading, group patterning, and group migration. A qualitative interpretation is also provided for these observations.

Creation and manipulation of optical Meron topologies in tightly focused electromagnetic field

The optical topology, which serves as a stable spatial electromagnetic structure, offers a new dimension for applications in the field of optical information processing, transmission, and storage. In recent years, there has been an increasing focus on these spatially structured light fields. By reversing the radiation of orthogonal dipole pairs, we propose an approach to generate Meron topologies within the focused light field while also investigating the evolution of the Meron structure along the longitudinal axis. Through introducing a dipole placed along the z-axis, we achieve precise positioning and fine adjustment of the topological center. The stability of Meron under a high numerical aperture objective lens (NA = 0.95) can be effectively demonstrated.

Combining six superluminal and subluminal structured light fields with right and left circular polarizations in a chiral medium through superposition

The structured vector fields of circularly polarized light, comprising both left and right (RCP and LCP) beams superposed in the atomic medium are investigated in this work. At resonance in the anomalous/normal dispersion area, both RCP and LCP beams with a non-negative and non-positive group index of ±40 have been recorded. RCP and LCP beam group velocities are enhanced to ±1.5×109m/s at δ=0.15Γ, that is surpassing the speed of light in vacuum, denoted as ”c” leading to superluminal propagation. The RCP is superluminal and the LCP subluminal at the resonance point of the probe field. The group delay for The LCP beam is positive and the RCP beam is non-positive. The worth of the group delay for RCP and LCP beams varies to ±4ns. The superposing structured vectors field of superluminal and subluminal circularly polarized light beams on the right and left ER,L(r,φ) are strong variation function of detuning of probe field δ/Γ, Rabi frequency of control field Λ3/Γ and phase of collective driving fields φ. The results are useful for the modification of powerful computers.

Vortex random lasing with tunable wavelength and orbital angular momentum

Random lasing with special structured light field has broad application prospects in various fields. However, the complex spatial modes of random lasing increase the difficulty of light field regulation and limit its practical application. Here, a vortex random lasing with dynamically tunable wavelength and orbital angular momentum is proposed based on the microfluidic channel. Different color random lasers are integrated into the same microfluidic channel for coarse control of the emission wavelengths from 462 to 685 nm by dynamically controlling the liquid flow. A special-shape cavity with a variable size of a gain region is further constructed to finely manipulate the emission wavelengths. Moreover, the vortex random lasing with tunable orbital angular momentum mode from −50 to 50 is realized. The results provide an outstanding strategy for generating the partially coherent vortex beams and may promote the practical applications of random lasers in the fields of sensing, imaging, and communication.

Topological atom optics and beyond with knotted quantum wavefunctions

Atom optics demonstrates optical phenomena with coherent matter waves, providing a foundational connection between light and matter. Significant advances in optics have followed the realization of structured light fields hosting complex singularities and topologically non-trivial characteristics. However, analogous studies are still in their infancy in the field of atom optics. Here, we investigate and experimentally create knotted quantum wavefunctions in spinor Bose–Einstein condensates which display non-trivial topologies. In our work we construct coordinated orbital and spin rotations of the atomic wavefunction, engineering a variety of discrete symmetries in the combined spin and orbital degrees of freedom. The structured wavefunctions that we create map to the surface of a torus to form torus knots, Möbius strips, and a twice-linked Solomon’s knot. In this paper we demonstrate close connections between the symmetries and underlying topologies of multicomponent atomic systems and of vector optical fields—a realization of topological atom-optics.

(3+1)-dimensional Pearcey-Gaussian wave packet with arbitrary velocity driven by flying focus.

The group velocity (GV) modulation of space-time wave packets (STWPs) along the transverse and longitudinal directions in free space is constrained by various factors. To surmount this limitation, a technique called "flying focus" has been developed, which enables the generation of laser pulses with dynamic focal points that can propagate at arbitrary velocities independent of GV. In this Letter, we propose a (3+1)-dimensional Pearcey-Gauss wave packet based on the "flying focus" technique, which exhibits superluminal propagation, transverse focus oscillation, and longitudinal periodic autofocusing. By selecting appropriate parameters, we can flexibly manipulate the position, the size, and the number of focal points- or make the wave packet follow a desired trajectory. This work may pave the way for the advancement of space-time structured light fields.

Metafiber transforming arbitrarily structured light

Structured light has proven useful for numerous photonic applications. However, the current use of structured light in optical fiber science and technology is severely limited by mode mixing or by the lack of optical elements that can be integrated onto fiber end-faces for wavefront engineering, and hence generation of structured light is still handled outside the fiber via bulky optics in free space. We report a metafiber platform capable of creating arbitrarily structured light on the hybrid-order Poincaré sphere. Polymeric metasurfaces, with unleashed height degree of freedom and a greatly expanded 3D meta-atom library, were 3D laser nanoprinted and interfaced with polarization-maintaining single-mode fibers. Multiple metasurfaces were interfaced on the fiber end-faces, transforming the fiber output into different structured-light fields, including cylindrical vector beams, circularly polarized vortex beams, and arbitrary vector field. Our work provides a paradigm for advancing optical fiber science and technology towards fiber-integrated light shaping, which may find important applications in fiber communications, fiber lasers and sensors, endoscopic imaging, fiber lithography, and lab-on-fiber technology.

Particle aggregation/disaggregation and sorting using woven spiral beams

Spiral beams (SBs) have attracted increasing attention in structured light fields owing to their chirality and rich modes. However, the wrench force of existing SBs is uncontrollable and nonadjustable, which greatly limits the complex applications of particle manipulation. To address this issue, we proposed a woven spiral beam (WSB) with a controllable force field. The WSB was constructed by reshaping multispiral beams woven through an SB. The proposed WSB has flexible adjustable intensity lobes, which are easy to modulate independently, including size, position, helicity, and phase gradient. Furthermore, the WSBs were used to experimentally execute important particle manipulations, such as aggregation/disaggregation and sorting. This study provides an alternative scheme for the functional applications of SBs, which leads to different application scenarios in optical manipulations.

Three-dimensional implementation of multi-mode fractional-order elliptical perfect optical vortex arrays

Fractional-order vortex beams possess unique spin and orbital angular momentum structure, and have significant applications in various fields. Nevertheless, the construction and tuning of these beams require high-precision optical devices and systems that are challenging to implement. Here, we propose a simple and effective method for realizing multi-mode independent modulation of fractional-order vector elliptical perfect optical vortices. The linear modulation of the EPOV ring is demonstrated. By combining the mode extraction with optical pen, multi-mode independent modulation of fractional-order elliptical perfect optical vortex arrays are successfully constructed, including position, quantity, ellipticity, topological charge, and polarization order. The experimental results are highly consistent with the numerical simulation results. We also demonstrate the implementation process of constructing multiple fractional-order EPOV arrays in three-dimensional space. This work provides a simple and feasible solution for the control of complex structured light fields and is expected to play an important role in optical trapping, optical communication, optical imaging, and quantum optics.

Low-cost printed holography for the generation ofstructured light.

Recently, the study of structured light fields has attracted great interest, which includes their generation and characterization techniques, as well as their application. Most of these techniques rely on the use of expensive devices, such as liquid crystal spatial light modulators or digital micromirror devices that also require specialized knowledge and software. In this work, we present a scheme for producing low-cost amplitude holograms for the generation of structured light fields. We demonstrate the feasibility of this technique by creating a variety of paraxial modes, such as the well-known Laguerre-Gaussian and Hermite-Gaussian beams. We also demonstrate the potential of our technique in solving the phase retrieval problem to generate 2D and 3D holographic images of objects. Finally, we compare our proposal with the typical generation techniques using digital micromirror devices. Our proposal will pave the path for the generation of structured light beams in more affordable ways for the application in undergrad laboratories.

Optical heating-induced spectral tuning of supercontinuum generation in liquid core fibers using multiwall carbon nanotubes.

In this work, we demonstrate the optical heating modulation of soliton-based supercontinuum generation through the employment of multi-walled carbon nanotubes (MW-CNTs) acting as fast and efficient heat generators. By utilizing highly dispersion-sensitive liquid-core fibers in combination with MW-CNTs coated to the outer wall of the fiber, spectral tuning of dispersive waves with response times below one second via exploiting the strong thermo-optic response of the core liquid was achieved. Local illumination of the MW-CNTs coated fiber at selected points allowed modulation of the waveguide dispersion, thus controlling the soliton fission process. Experimentally, a spectral shift of the two dispersive waves towards the region of anomalous dispersion was observed at increasing temperatures. The presented tuning concept shows great potential in the context of nonlinear photonics, as complex and dynamically reconfigurable dispersion profiles can be generated by using structured light fields. This allows investigating nonlinear frequency conversion processes under unconventional conditions, and realizing nonlinear light sources that are reconfigurable quickly.

Abnormally autofocusing vortex Swallowtail Gaussian vector beam with low spatial coherence

The precondition for the application of light beams is the ability to devise light distribution with high precision. Controlling more dimensions for structured light fields is an effective method to improve the ability to devise light distribution. The Swallowtail beam, due to its rich regulatory parameters, provides the possibility to design a light field with a specific intensity distribution. Utilizing the Swallowtail beam as a foundation, we design its initial phase, polarization, and coherent structure, and propose a partially coherent azimuthally polarized circular vortex Swallowtail Gaussian beam (PCAPCVSGB) in our paper. This beam exhibits an abnormal self-focusing ability and forms an easily adjustable optical potential well at the focal plane, providing another effective tool for achieving optical manipulation. In addition, the PCAPCVSGB also shows an interesting vector property. It possesses a stable polarization singularity even with changes in coherence and topological charges, which exhibits a potential application value in optical communication.

Mid-infrared vortex array generation with a tunable singularity in an Er:YAP laser

Optical vortex arrays are structured light fields with multiple phase singularities that have attracted considerable attention in recent years. Here, we demonstrate the direct generation of an optical vortex array with tunable singularity from a mid-infrared Er: yttrium aluminum perovskite laser under the annular-pumping regime. An axicon combined with a plano–convex lens is used to reshape the pumping beam into an annular one to match the different orders of the Laguerre–Gaussian mode. By adjusting the pump power and the lateral displacement of the gain medium, a tunable vortex array with one to four singularities is obtained in the ∼3-μm mid-infrared wavelength region. The lasing characteristics of the mid-infrared vortex arrays are evaluated and discussed. The experimental results can shed some light on the generation of mid-infrared optical vortex laser arrays and their applications.