Physical Optics|101 Article(s)
Propagation dynamics of a spatiotemporal vortex pulse in the spatial fractional system
Jinqi Song, Fengqi Liu, Mingli Sun, Xiangyu Tong, Naichen Zhang, Bingsong Cao, Wenzhe Wang, Kaikai Huang, Xian Zhang, and Xuanhui Lu
The dynamics of wave packets carrying a spatiotemporal vortex in the spatial fractional system is still an open problem. The difficulty stems from the fact that the fractional Laplacian derivative is essentially a nonlocal operator, and the vortex is space-time coupled. Here, we investigate the transmission of spatiotemporal vortices in the spatial fractional wave equation (FWE) and demonstrate the effects of linewidth, vortex topological charge, and linear chirp modulation on the transmission of Bessel-type spatiotemporal vortex pulses (BSTVPs). Under narrowband conditions, we find that the propagation of BSTVP in the FWE can be seen as the coherent superposition of two linearly shifted half-BSTVPs and can reveal orbital angular momentum backflow for the half-BSTVP. Our analysis can be extended to other spatiotemporal vortex pulses.
Photonics Research
  • Publication Date: Aug. 30, 2024
  • Vol. 12, Issue 9, 2027 (2024)
Optical edge-to-screw singularity state conversions
Haolin Lin, Junhui Jia, Guohua Liu, Yanwen Hu, Zhen Li, Zhenqiang Chen, and Shenhe Fu
Optical singularity states, which significantly affect propagation properties of light in free space or optical medium, can be geometrically classified into screw and edge types. These different types of singularity states do not exhibit direct connection, being decoupled from each other in the absence of external perturbations. Here we demonstrate a novel optical process in which a higher-order edge singularity state initially nested in the propagating Gaussian light field gradually involves into a screw singularity with a new-born topological charge determined by order of the edge state. The considered edge state comprises an equal superposition of oppositely charged vortex and antivortex modes. We theoretically and experimentally realize this edge-to-screw conversion process by introducing intrinsic vortex–antivortex interaction. We also present a geometrical representation for mapping this dynamical process, based on the higher-order orbital Poincaré sphere. Within this framework, the edge-to-screw conversion is explained by a mapping of state evolution from the equator to the north or south pole of the Poincaré sphere. Our demonstration provides a novel approach for manipulating singularity state by the intrinsic vortex–antivortex interactions. The presented phenomenon can be also generalized to other wave systems such as matter wave, water wave, and acoustic wave.
Photonics Research
  • Publication Date: Jul. 26, 2024
  • Vol. 12, Issue 8, 1689 (2024)
Rotational Doppler effect of composite vortex beams with tailored OAM spectra
Yutian Liang, Ruijian Li, Jie Zhao, Xingyuan Lu, Tong Liu, Zhengliang Liu, Yuan Ren, and Chengliang Zhao
There recently has been increasing interest in the research and application of the rotational Doppler effect (RDE), which paves a promising way to detect rotating objects remotely. In order to obtain more information about the rotating object from the rotational Doppler signal, composite vortex beams by coaxial superposition of orbital angular momentum (OAM) modes are often used as the probe beam. However, to the best of our knowledge, the RDE of composite vortex beams with arbitrary OAM spectra has not yet been comprehensively studied. In this paper, the correspondence between the OAM spectrum of a probe beam and the frequency spectrum of a rotational Doppler signal is theoretically analyzed. It is explicitly revealed that the RDE frequency spectrum of scattered light is related to the product of two autocorrelation functions: one from the OAM spectrum of probe beam and the other from the spiral spectrum of rotating object. On the basis of this relation, one can regulate the RDE frequency spectrum on demand via tailoring the OAM spectrum of the probe beam. As a proof of concept we design a special composite vortex beam to eliminate the broadening of the RDE spectrum induced by misalignment. These findings are of practical value in applications such as remote sensing and optical metrology.
Photonics Research
  • Publication Date: Jul. 26, 2024
  • Vol. 12, Issue 8, 1665 (2024)
Controllable split polarization singularities for ultra-precise displacement sensing
Jiakang Zhou, Haixiang Ma, Shuoshuo Zhang, Wu Yuan, Changjun Min, Xiaocong Yuan, and Yuquan Zhang
The topic of optical precise displacement measurement has garnered significant attention and generated widespread interest recently. The use of optical singularity offers a potential solution for this purpose, although effectively manipulating the singularity in an ideal manner remains challenging. In this work, we propose a theoretical approach to achieve controllable position modulation of the C-point in the focal plane, whose spatial position can be easily modulated by adjusting the relative offset factor β and the offset angle α of an azimuthal polarization beam (APB), while the interval and orientation of the C-points can be flexibly regulated. Notably, the chiral polarization state undergoes a distinct reversal along the link-line connecting the two C-points, thereby providing a promising approach for accurate displacement sensing. To evaluate its sensing characteristics, the varying pattern of the scattered field intensity is monitored when sweeping a gold helix and nanoparticle along the link-line. The results of simulation quality index Q verify that the equilibrium factor of the scattering field possesses an obvious linear relationship with the displacement, signifying a precise sub-nanometric sensitivity. This research introduces new methods for the flexible control of polarization singularities in tightly focused fields, thereby enhancing the utilization of circular polarization properties near C-points for displacement sensing. These findings not only enrich the field of nanometer measurement technology but also pave the way for new avenues of research in this domain.
Photonics Research
  • Publication Date: Jul. 01, 2024
  • Vol. 12, Issue 7, 1478 (2024)
Dual-curvilinear beam enabled tunable manipulation of high- and low-refractive-index particles
Zheng Yuan, Chenchen Zhang, Yuan Gao, Wenxiang Yan, Xian Long, Zhi-Cheng Ren, Xi-Lin Wang, Jianping Ding, and Hui-Tian Wang
We present an innovative approach for the simultaneous agile manipulation of high-refractive-index (HRI) and low-refractive-index (LRI) particles. Our method involves introducing a dual-curvilinear optical vortex beam (DC-OVB) generated by superimposing a pair of curved beams: HRI and LRI particles are controlled by the bright curve and the dark channel between the two curves, respectively. The proposed DC-OVB provides customizable motion paths and velocities for both LRI and HRI particles. Each curve of the DC-OVB can support a distinct orbital flow density (OFD), enabling the application of torques to HRI and LRI particles, guiding them to orbit along specified trajectories and prompting them to execute various curvilinear motions simultaneously, including curvilinear movement, revolution, and rotation.
Photonics Research
  • Publication Date: Jun. 14, 2024
  • Vol. 12, Issue 7, 1427 (2024)
Manipulation of low-refractive-index particles using customized dark traps
Minru He, Yansheng Liang, Xue Yun, Shaowei Wang, Tianyu Zhao, Linquan Guo, Xinyu Zhang, Shiqi Kuang, Jinxiao Chen, and Ming Lei
Low-refractive-index particles play significant roles in physics, drug delivery, biomedical science, and other fields. However, they have not attained sufficient utilization in active manipulation due to the repulsive effect of light. In this work, the establishment of customized dark traps is demonstrated to fulfill the demands of versatile manipulation of low-refractive-index particles. The customized dark traps are generated by assembling generalized perfect optical vortices based on the free lens modulation method, by which the beams’ shape, intensity, and position can be elaborately designed with size independent of topological charge. Using the customized dark traps with high quality and high efficiency, rotation along arbitrary trajectories with controllable speed, parallel manipulation, and sorting of low-refractive-index particles by size can be realized. With unprecedented flexibility and quality, the customized dark traps provide tremendous potential in optical trapping, lithography, and biomedicine.
Photonics Research
  • Publication Date: May. 31, 2024
  • Vol. 12, Issue 6, 1334 (2024)
Probing phase transition of band topology via radiation topology
Chang-Yin Ji, Wenze Lan, Peng Fu, Gang Wang, Changzhi Gu, Yeliang Wang, Jiafang Li, Yugui Yao, and Baoli Liu
Topological photonics has received extensive attention from researchers because it provides brand new physical principles to manipulate light. Band topology is characterized using the Berry phase defined by Bloch states. Until now, the scheme for experimentally probing the topological phase transition of band topology has always been relatively lacking in topological physics. Moreover, radiation topology can be aroused by the far-field polarization singularities of Bloch states, which is described by the Stokes phase. Although such two types of topologies are both related to Bloch states on the band structures, it is rather surprising that their development is almost independent. Here, in optical analogs of the quantum spin Hall effects (QSHEs) and Su-Schrieffer-Heeger model, we reveal the correlation between the phase transition of band topology and radiation topology and then demonstrate that the radiation topology can be employed to study the band topological transition. We experimentally demonstrate such an intriguing phenomenon in optical analogs of QSHEs. Our findings not only provide an insightful understanding of band topology and radiation topology, but also can serve as a route to manipulate light.
Photonics Research
  • Publication Date: May. 17, 2024
  • Vol. 12, Issue 6, 1150 (2024)
Highly efficient nonuniform finite difference method for three-dimensional electrically stimulated liquid crystal photonic devices
Zhenghao Guo, Mengjun Liu, Zijia Chen, Ruizhi Yang, Peiyun Li, Haixia Da, Dong Yuan, Guofu Zhou, Lingling Shui, and Huapeng Ye
Liquid crystal (LC) photonic devices have attracted intensive attention in recent decades, due to the merits of tunability, cost-effectiveness, and high efficiency. However, the precise and efficient simulation of large-scale three-dimensional electrically stimulated LC photonic devices remains challenging and resource consuming. Here we report a straightforward nonuniform finite difference method (NFDM) for efficiently simulating large-scale LC photonic devices by employing a spatially nonuniform mesh grid. We show that the NFDM can be further accelerated by approximately 504 times by using the improved successive over-relaxation method (by 12 times), the symmetric boundary (by 4 times), the momentum gradient descent algorithm (by 3.5 times), and the multigrid (by 3 times). We experimentally fabricated the large-scale electrically stimulated LC photonic device, and the measured results demonstrate the effectiveness and validity of the proposed NFDM. The NFDM allocates more grids to the core area with steep electric field gradient, thus reducing the distortion of electric field and the truncation error of calculation, rendering it more precise than the finite element method and traditional finite difference method with similar computing resources. This study demonstrates an efficient and highly reliable method to simulate the large-scale electrically stimulated LC photonic device, and paves the way for customizing a large-scale LC photonic device with designable functionalities.
Photonics Research
  • Publication Date: Apr. 01, 2024
  • Vol. 12, Issue 4, 865 (2024)
From non-scattering to super-scattering with Mie-tronics|Editors' Pick
Hooman Barati Sedeh, and Natalia M. Litchinitser
Electric anapoles, arising from the destructive interference of primitive and toroidal electric dipole moments, have recently emerged as a fundamental class of non-scattering sources. On the other hand, super-scattering states represent the opposite regime wherein the scattering cross-section of a subwavelength particle exceeds the single-channel limit, leading to a strong scattering behavior. Here, we demonstrate that the interplay between the topology of light and the subwavelength scatterer can lead to these two opposite responses within an isolated all-dielectric meta-atom. In particular, we present the emergence of a new non-scattering state, referred to as hybrid anapole, which surpasses conventional electric dipole anapoles by achieving a remarkable 23-fold enhancement in the suppression of far-field radiation and almost threefold enhancement in the confinement of electromagnetic energy inside the meta-atom. We also explore the role of particle orientation and its inversion symmetry in the scattering response and predict the possibility of switching between non-scattering and super-scattering states within the same platform. The presented study elucidates the role of light and matter topologies in the scattering response of subwavelength meta-atoms, uncovering two opposite regimes of light-matter interaction and opening new avenues in applications such as nonlinear optics and spectroscopy.
Photonics Research
  • Publication Date: Mar. 13, 2024
  • Vol. 12, Issue 4, 608 (2024)
Indefinite metacavities coupled to a mirror: bound states in the continuum with anomalous resonance scaling
Qiang Zhang, Peixiang Li, Zhiyuan Gu, Shaoding Liu, and Zejun Duan
Indefinite metacavities (IMCs) made of hyperbolic metamaterials show great advantages in terms of extremely small mode volume due to large wave vectors endowed by the unique hyperbolic dispersion. However, quality (Q) factors of IMCs are limited by Ohmic loss of metals and radiative loss of leaked waves. Despite the fact that Ohmic loss of metals is inevitable in IMCs, the radiative loss can be further suppressed by leakage engineering. Here we propose a mirror coupled IMC structure which is able to operate at Fabry–Pérot bound states in the continuum (BICs) while the hyperbolic nature of IMCs is retained. At the BIC point, the radiative loss of magnetic dipolar cavity modes in IMCs is completely absent, resulting in a considerably increased Q factor (>90). Deviating from the BIC point, perfect absorption bands (>0.99) along with a strong near-field intensity enhancement (>1.8×104) appear when the condition of critical coupling is almost fulfilled. The proposed BICs are robust to the geometry and material composition of IMCs and anomalous scaling law of resonance is verified during the tuning of optical responses. We also demonstrate that the Purcell effect of the structure can be significantly improved under BIC and quasi-BIC regimes due to the further enhanced Q factor to mode volume ratio. Our results provide a new train of thought to design ultra-small optical nanocavities that may find many applications benefitting from strong light–matter interactions.
Photonics Research
  • Publication Date: Mar. 01, 2024
  • Vol. 12, Issue 3, 598 (2024)
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