Search Results (224)

Light carrying orbital angular momentum (OAM) has emerged as a promising tool for manipulating light–matter interactions, providing an additional degree of freedom to explore chiral-optical phenomena at the nanoscale. When such vortex beams interact with chiral metamaterials, a unique phenomenon of optical asymmetry known as vortical dichroism (VD) arises. Nevertheless, most existing chiral metamaterials exhibit limited VD responses, and the underlying physical mechanisms are yet to be fully clarified. In this work, we propose three-dimensional spiral metamaterials that achieve gigantic VD effect. This pronounced VD effect originates from the intrinsic coupling between the spiral structure and the chirality inherent to optical vortices, which leads to strongly asymmetric scattering intensities for left- and right-handed OAM beams of opposite topological charges. Numerical simulations confirm a remarkable VD value of 0.69. Further analysis of electric field distributions reveals that the asymmetric VD response stems from a handedness-dependent excitation of distinct electromagnetic modes. For opposite handedness, spatial mode mismatch results in enhanced scattering. In contrast, matching handedness enables efficient energy coupling into a guided spiral mode, which suppresses scattering. These findings not only deepen the physical understanding of VD mechanisms but also establish a versatile platform for developing advanced chiral photonic devices and enhancing OAM-based light–matter interactions. Full article

Manipulating complex light fields through highly anisotropic scattering medium (HASM) remains a fundamental challenge due to the intricate underlying physics and broad application potential. We introduce a unified theoretical and experimental framework for generating and controlling arbitrarily polarized curved caustic beams using an extended polarization transfer matrix (EPTM) for the first time, enabling intuitive polarization transformation through HASM. The EPTM is experimentally measured via a four-step phase-shifting technique, and its submatrices are independently modulated with tailored caustic phase profiles. This strategy facilitates the creation of diverse high-resolution caustic beams, including Gaussian and vortex types with tunable energy distribution, polarization states, and vorticity. The achievement of polarization transformation through HASM by our approach offers versatile manipulation over optical field properties such as multiple high-resolution caustic beams, angular momentum flux, and polarization, paving the way for enhanced functionality in advanced optical systems. Full article

Over the past thirty years, the focus in singular optics has been on structured beams carrying orbital angular momentum (OAM) for diverse applications in science and technology. However, as practice has shown, the OAM-free structured Gaussian beams with several degrees of freedom are no worse than the OAM beams, especially when propagating through turbulent flows. In this paper, we partially fillthis gap by theoretically and experimentally mapping cyclic changes in vortex-free states (including OAM) as a phase portrait of the beam evolution in an astigmatic optical system. We show that those cyclic variations in the beam parameters are accompanied by the accumulation of the geometric Berry phase, which is an additional degree of freedom. We find also that the geometric phase of cyclic changes in the intensity ellipse shape does not depend on the radial numbers of the Laguerre–Gaussian mode with zero topological charge and is always set by changing the shape of the Gaussian beam. The Stokes parameter formalism was developed to map the beam states’ evolution onto a Poincaré sphere based on physically measurable second-order intensity moments. Theory and experiment are found to be in a good enough agreement. Full article

Based on the extended Huygens–Fresnel principle and mode expansion theory, we derive the expression for the Coherence-Orbital Angular Momentum (COAM) matrix of twisted Gaussian Schell-model (TGSM) beams propagating through non-Kolmogorov turbulence. Using numerical simulations, we compare the evolution characteristics of the COAM matrix in free space and under non-Kolmogorov turbulence conditions. The study analyzes the variation patterns in the absolute values, real parts, and imaginary parts of the COAM matrix elements under different topological charges, and provides a detailed investigation of the influence of various beam parameters and turbulence parameters on these elements. The results show that by selecting appropriate parameters, the negative impact of turbulence on the correlation between orbital angular momentum (OAM) modes can be effectively mitigated. This work provides theoretical support for parameter selection and optimization in atmospheric optical communication systems. Full article

Spin angular momentum is a fundamental dynamical property of elementary particles and fields, playing a critical role in light–matter interactions. In optical studies, the optical spin angular momentum is closely linked to circular polarization. Research on the interaction between optical spin and matter or structures has led to numerous novel optical phenomena and applications, giving rise to the emerging field of spin optics. Historically, researchers primarily focused on longitudinal optical spin aligned parallel to the mean wavevector. In recent years, investigations into the spin–orbit coupling properties of confined fields—such as focused beams, guided waves, and evanescent waves—have revealed a new class of optical spin oriented perpendicular to the mean wavevector, referred to as optical transverse spin. In the optical near-field, such transverse spins arise from spatial variations in the momentum density of confined electromagnetic waves, where strong coupling between spin and orbital angular momenta leads to various topological spin structures and properties. Several reviews on optical transverse spin have been published in recent years, systematically introducing its fundamental concepts and the configurations that generate it. In this review, we detail recent advances in spin optics from three perspectives: theory, experimental techniques, and applications, with a particular emphasis on the fundamental physics of transverse spin and the resulting topological structures and characteristics. The conceptual and theoretical framework of spin optics is expected to significantly support further exploration of optical spin-based applications in fields such as optics imaging, topological photonics, metrology, and quantum technologies. Furthermore, these principles can be extended to general classical wave systems, including fluidic, acoustic, and gravitational waves. Full article

Based on the birefringence phenomenon of vortex beam in uniaxial crystals for optical path design, yttrium vanadate crystals and waveplates are used to realize coherent mixing of vortex beam. A crystal-type spatial light mixer applied to a vortex beam communication system is designed. The effects of beam polarization, waveplate optical axis, crystal transmittance, and other factors on the performance of the mixer are explored. Simulations show that the mixer output phase error is extremely small, the insertion loss is about 1.9 $\mathrm{dB}$ , and the overall loss is close to 36.6%. Finally, it is applied in the vortex optical coherent communication system, and the effectiveness of the optical mixer is experimentally verified with a phase deviation of 3°, a splitting ratio close to 1, and a mixing efficiency of 78.5%. Vortex beam mixer extracts information such as phase, amplitude, and polarization of the signal light by combining optical beams with orbital angular momentum modes. It enables mode multiplexing, topologically protected transmission, and high-order modulation. This technology is widely applied in space optical communication, high-speed fiber-optic systems, and quantum communication. Full article

Laser-induced breakdown spectroscopy (LIBS), limited by matrix effects, self-absorption in complex samples, and ambient atmospheric influences, still requires further improvement in detection sensitivity and signal stability. In this work, the excitation beam of LIBS is modulated into an optical vortex by an optical phase element, and optical vortex-induced LIBS is used to detect and analyze coal samples. Building on the uniform annular intensity distribution and orbital angular momentum (OAM) carried by the optical vortex, it is anticipated that spectral signal intensity can be enhanced by improving plasma ablation efficiency, reducing shielding effects, and increasing electron collision frequency, thereby reducing signal uncertainty and enhancing LIBS analytical performance. For the first time, a classification model combining principal component analysis (PCA) and support vector machine (SVM) is developed, integrating optical vortex-induced LIBS technology with machine learning. Using the PCA-SVM model, optical vortex-based LIBS attained a coal classification accuracy of 95%, significantly higher than the 88% achieved with Gaussian beams, thereby markedly improving classification performance for complex matrix samples. These results demonstrate that optical vortex-induced LIBS possesses strong potential for efficient detection of samples with complex matrices. Full article

We study the quantum dynamics of cold atoms initially confined in a helical optical tube (HOT) and subsequently released into free space. This helicoidal potential, engineered via structured light fields with orbital angular momentum, imposes a twisted geometry on the atomic ensemble during confinement. We examine how this geometry shapes the initial quantum state—particularly its spatial localization and phase structure—and how these features influence the subsequent free evolution. Our analysis reveals that the overall confinement geometry supports the formation of spatially coherent, structured wavepackets, paving the way for the realization of twisted Bose–Einstein condensates and directed atom lasers. The results are of particular interest for applications in quantum technologies, such as coherent atom beam shaping, matter-wave interferometry, and guided transport of quantum matter. Full article

Orbital Angular Momentum (OAM) of light is generating growing interest within the scientific community. This entry reviews the origins and applications of OAM. It is the counterpart of linear momentum for systems in rotation. The general expression of OAM is discussed, followed by its implications in terms of phase distribution and donut-shaped intensity profiles. Applications described include the generation of optical torque, telecommunications enhancement, and the rotational Doppler effect, emphasizing the role and consequences of angular momentum. In particular, its use to manipulate systems or to detect rotations is described. Finally, further developments and technological barriers are considered. Full article

As extensions of circular symmetric vortex beams, elliptical vortex beams with more diverse field forms are worthy of attention. In this paper, we investigate the mode propagation characteristics of an elliptical perfect optical vortex (EPOV) beam in oceanic turbulence. The theoretical model is constructed to analyze the detection probability of orbital angular momentum mode and average capacity at the receiver. The results reveal that the self-focusing property of the EPOV beam is able to improve propagation performance. By changing the elliptical scaling factor and the ratio of ring radius to width, the self-focusing effect is adjustable. The smaller elliptical scaling factor and ring radius to width ratio are beneficial for short-range transmission, while the larger ones are better for long-range transmission. Furthermore, the impacts of oceanic temperature and salinity in wide variation ranges are analyzed by use of the oceanic turbulence optical power spectrum. Higher capacity is obtained when the EPOV beam propagates in low-temperature and low-salinity oceanic channel. The research is referable for the design of underwater communication systems. Full article

High-order linear polarization (LP) modes and vortex beams carrying orbital angular momentum (OAM) are highly useful in various fields. High-order LP modes provide higher thresholds for nonlinear effects, reduced sensitivity to distortions, and better energy extraction in high-power lasers. OAM beams are useful in optical communication, imaging, particle manipulation, and fiber sensing. The ability to switch between these mode outputs enhances system versatility and adaptability, supporting advanced applications both in research and industry. This paper presents the design of a 19 × 1 photonic lantern capable of outputting 19 LP modes and 16 OAM modes with low loss. Using the beam propagation method, we simulated and analyzed the mode evolution process and insertion loss, and we calculated the transmission matrix of the photonic lantern. The results indicate that the designed device can efficiently evolve into these modes with a maximum insertion loss not exceeding 0.07 dB. Furthermore, an adaptive control system was developed by introducing a mode decomposition system at the output and combining it with the Stochastic Parallel Gradient Descent (SPGD) + basin hopping algorithm. Simulation results show that this system can produce desired modes with over 90% mode content, demonstrating promising application prospects in switchable high-order mode systems. Full article

To address the issues of limited orbital angular momentum (OAM) mode count, poor transmission quality, and complex cladding structures in ring-core photonic crystal fibers, a novel OAM-supporting ring-core anti-resonant photonic crystal fiber is designed. This fiber features a high-index-doped ring-core surrounded by a three-layer anti-resonant nested tube cladding. Numerical simulations based on the finite element method indicate that the designed fiber has the ability to reliably transmit up to 90 OAM modes within the wavelength range of 1530–1620 nm. Additionally, this fiber demonstrates outstanding performance characteristics, achieving a peak effective refractive index difference of 0.0041 while maintaining remarkably low confinement loss between 10⁻¹² dB/m and 10⁻⁸ dB/m. The minimum effective mode field area is 101.41 μm², and the maximum nonlinear coefficient is 1.05 W⁻¹·km⁻¹. The dispersion is flat, with a minimum dispersion variation of merely 0.5394 ps/(nm·km). The mode purity is greater than 98.5%, and the numerical aperture ranges from 0.0689 to 0.089. The designed OAM-supporting ring-core anti-resonant photonic crystal fiber has broad application prospects in long-haul optical communication and high-speed data transmission. Full article

In this paper, we design a new type of terahertz orbital angular momentum (OAM) optical fiber with excellent transmission characteristics over a wide frequency range. Within the 0.8–1.8 THz frequency band, it shows stable support for transmission of the fifth-order OAM mode. Its dispersion control effect is excellent; it maintains the confinement loss of most modes at the extremely low level of 10⁻¹⁰ dB/m; its maximum dispersion is only 5.57 ps/THz/cm; and its effective mode field area is greater than 1.11 × 10⁻⁷ m². These characteristics jointly endow this optical fiber with broad application prospects and significant research value in the field of terahertz communication. With the continuous advancement of technology in this field, this optical fiber is expected to become a key component when building efficient, reliable, and large-capacity communication systems. Full article

A novel encoding method based on the orbital angular momentum (OAM) mode and radial mode of composite vortex beams is proposed. The superposition of two vortex beams generates 32 different types of composite vortex beams: one of them is a Laguerre–Gaussian (LG) beam with a fixed OAM mode and radial mode, and the other is a LG beam containing four radial modes (p = 0, 1, 2, 3) and eight OAM modes with the same interval (l = ±3, ±5, ±7, ±9). A specially designed composite fork-shaped grating (CFG) is utilized to generate the intensity array pattern, and the received composite vortex beam is diffracted into a Gaussian beam with the relevant coordinates. Based on the coordinates and the number of bright rings in the intensity pattern, the OAM modes and radial modes of the two vortex beams composing the superposition state are determined, and finally the received composite vortex beam is decoded into the initially propagated information sequence. The correctness and effectiveness of the proposed encoding are confirmed through the comparative analysis of the correlation of the optical fields at both the transmitter and receiver in the two scenarios of interval and non-interval encoding. The proposed encoding method can significantly improve the efficiency of information transmission and its resistance to interference, holding great potential for future applications in free-space optical communication. Full article

The rapid growth of data traffic in modern communication networks has led to the development of advanced high-capacity multiplexing methods. Orbital angular momentum (OAM)–based mode division multiplexing (MDM) offers a promising scheme by utilizing the orthogonality of helical phase modes to transmit independent data streams simultaneously. In this work, we introduce a novel adjacent mode separation method exploiting OAM’s concentric intensity characteristics for free-space optical (FSO) spatial multiplexing. This method enables the detection of each OAM channel based on its distinctive ring-shaped intensity distribution, contrary to the conventional on-axis phase flattening approach. Two spatially multiplexed signals with different modes are separated by aligning its concentric intensity ring with the active area of an avalanche photodiode (APD), effectively suppressing crosstalk from adjacent modes. Experimental measurements demonstrate that our method achieves a bit-error-rate (BER) performance not exceeding the forward error correction (FEC) threshold, $3.8\times {10}^{-3}$, at up to 160 Mbps of data rate, while the conventional detection scheme fails beyond 5 Mbps. The analysis of the eye diagram confirms that our concentric-ring demultiplexing system achieves a high signal-to-noise ratio (SNR) and mode selectivity. These results support the feasibility of the proposed concentric intensity-based mode separation methodology for constructing compact, high-throughput OAM-multiplexed FSO links. Full article