Fractional vortex beams exhibit a higher degree of modulation dimensions than conventional vortices, thus inheriting superior anti-turbulent transmission properties through the incorporation of additional coherence modulation. However, aliasing the mixed modes induced by coherence degradation makes the quantitative measurement of the topological charge in fractional vortex beams challenging. In this study, a coherence phase spectrum was introduced, and experimental demonstrations to quantitatively determine the fractional topological charge of partially coherent fractional vortex beams were performed. By leveraging the four-dimensional measurement of a partially coherent light field, the source coherence function was inversely reconstructed, and fractional topological charges were determined with high precision by extracting the phase spectrum of the coherence function. Laguerre–Gaussian, elliptical Gaussian, and plane-wave-fraction vortex beams with various degrees of coherence were used to demonstrate measurement precision. The proposed method is applicable to X-rays and electron vortices. It has potential applications in optical encryption, high-capacity optical communication, and quantum entanglement.

In this study, we present a method for free-space beam shaping and steering based on a silicon optical phased array, which addresses the theoretical limitation of traditional bulk optics. We theoretically analyze the beam propagation properties with changes in the applied phase. Different beam profiles can be shaped by varying the phase combination, while a high-order quasi-Bessel beam can be generated with a cubic change to the phase modulation. The simulated results are validated further experimentally, and they match one another well. Beam steering can be achieved with a field of view as large as 140°, which has potential benefits for practical applications. The presented method is expected to have broad application prospects for optical communications, free-space optical interconnects, and light detection and ranging.

Optical skyrmions are quasiparticles with nontrivial topological textures that have significant potential in optical information processing, transmission, and storage. Here, we theoretically and experimentally achieve the conversion of optical skyrmions among Néel, Bloch, intermediate skyrmions, and bimerons by polarization devices, where the fusion and annihilation of optical skyrmions are demonstrated accordingly. By analyzing the polarization pattern in Poincaré beams, we reveal the skyrmion topology dependence on the device, which provides a pathway for the study of skyrmion interactions. A vectorial optical field generator is implemented to realize the conversion and superposition experimentally, and the results are in good agreement with the theoretical predictions. These results enhance our comprehension of optical topological quasiparticles, which could have a significant impact on the transfer, storage, and communication of optical information.

We propose a new type of dispersion-flattened waveguide without a slot-assisted structure that can obtain an ultra-flat group velocity dispersion profile with five or six zero-dispersion wavelengths in the mid-infrared region. The dispersion profile becomes less sensitive to the waveguide dimensions due to the absence of the slot-assisted structure, making waveguide fabrication more friendly. The dispersion profile varies between -0.472 and 0.365ps/(nm · km) over a 2665 nm bandwidth from 2885 nm to 5550 nm with a flatness of 3183.99 nm² · km/ps. Two different combinations of materials are demonstrated for dispersion flattening of the proposed waveguide structures. We also provide design guidance for the proposed waveguide structures with other combinations of materials.

利用Debye积分，研究了三个相互正交的轨道角动量（包括两个正交的横向轨道角动量以及一个纵向轨道角动量）光场在紧聚焦条件下的复杂耦合现象，并演示了焦场中相位奇点在三维时空间中的演化。此外，还研究了具有不同拓扑荷数的纵向轨道角动量对聚焦波包整体轨道角动量指向的影响。数值结果表明，聚焦波包的整体轨道角动量指向可由纵向轨道角动量的拓扑荷数进行调控，进而实现紧聚焦时空波包的轨道角动量指向可控。这种角动量指向可控的时空波包在光学微操作、微纳加工、自旋-轨道耦合以及量子通信等领域具有潜在的应用价值。

Spatiotemporal optical vortex (STOV) wavepacket carrying transverse photonic orbital angular momentum (OAM) has been extensively studied in the past few years. In this Letter, we propose and study a novel STOV wavepacket with multiple phase singularities embedded in different space–time domains using analytical and numerical approaches. By tuning different parameters used for designing the wavepacket, it is possible to engineer both the magnitude and orientation of the photonic OAM in space–time. The vectorially controllable OAM will pave new avenues and facilitate applications such as novel optical communication, studying complicated quantum systems, and spin-and-OAM interactions.

Spectral fingerprint and terahertz (THz) field-induced carrier dynamics demands the exploration of broadband and intense THz signal sources. Spintronic THz emitters (STEs), with high stability, a low cost, and an ultrabroad bandwidth, have been a hot topic in the field of THz sources. One of the main barriers to their practical application is lack of an STE with strong radiation intensity. Here, through the combination of optical physics and ultrafast photonics, the Tamm plasmon coupling (TPC) facilitating THz radiation is realized between spin THz thin films and photonic crystal structures. Simulation results show that the spectral absorptance can be increased from 36.8% to 94.3% for spin THz thin films with TPC. This coupling with narrowband resonance not only improves the optical-to-spin conversion efficiency, but also guarantees THz transmission with a negligible loss (∼4%) for the photonic crystal structure. According to the simulation, we prepared this structure successfully and experimentally realized a 264% THz radiation enhancement. Furthermore, the spin THz thin films with TPC exhibited invariant absorptivity under different polarization modes of the pump beam and weakening confinement on an obliquely incident pump laser. This approach is easy to implement and offers possibilities to overcome compatibility issues between the optical structure design and low energy consumption for ultrafast THz opto-spintronics and other similar devices.

Spatiotemporal optical vortex (STOV) pulses can carry transverse orbital angular momentum (OAM) that is perpendicular to the direction of pulse propagation. For a STOV pulse, its spatiotemporal profile can be significantly distorted due to unbalanced dispersive and diffractive phases. This may limit its use in many research applications, where a long interaction length and a tight confinement of the pulse are needed. The first demonstration of STOV pulse propagation through a few-mode optical fiber is presented. Both numerical and experimental analysis on the propagation of STOV pulse through a commercially available SMF-28 standard telecommunication fiber is performed. The spatiotemporal phase feature of the pulse can be well kept after the pulse propagates a few-meter length through the fiber even with bending. Further propagation of the pulse will result in a breakup of its spatiotemporal spiral phase structure due to an excessive amount of modal group delay dispersion. The stable and robust transmission of transverse photonic OAM through optical fiber may open new opportunities for transverse photonic OAM studies in telecommunications, OAM lasers, and nonlinear fiber-optical research.

The chiral feature of an optical field can be evaluated by the parameter of g-factor enhancement, which is helpful to enhance chiroptic signals from a chiral dipole. In this work, the superchiral spot has been theoretically proposed in metal-insulator-metal waveguides. The g-factor enhancement of the superchiral spot can be enhanced by 67-fold more than that of circularly polarized light, and the spot is confined in the deep wavelength scale along each spatial dimension. Moreover, the position of the superchiral spot can be tuned by manipulating the incident field. The tunable superchiral spot may find applications in chiral imaging and sensing.