随着大数据时代的到来，空间光通信已被广泛应用于各种通信系统中，但随之而来的是容量瓶颈的挑战。基于光场频率、时间、偏振、横向空间模式等维度调控的信息编解码方法在解决容量问题方面展现了优异性能，但光场的纵向维度却未被应用于信息编解码。针对此问题，本文提出了一种基于电介质超表面的光场纵向维度信息编解码新方法，基于四原子结构的几何相位和传输相位联合调控，实现了透射场自旋相关的复振幅调控。同时，利用光学冻结波原理产生了轨道角动量模式叠加态的纵向可控变化，并验证了光场模态的纵向调控能够以指数级提升信道中的模态容量。纵向维度作为一个全新的编码自由度，有望进一步提高自由空间光通信性能。

The spin Hall effect of a light beam is essentially a product of circular birefringence but is rarely demonstrated. Here, we provide a scheme for initiating off-axis circular birefringence based on the spin-dependent wave vector bifurcation of Bessel beams via a single liquid crystal Pancharatnam–Berry phase element. The tilted Bessel beam shows a detectable photonic spin Hall effect. By introducing the nonlinear propagation trajectories, the spin Hall effect is greatly enhanced. More surprisingly, the two spin states exactly propagate along the scaled trajectories, enabling flexible control of the spin separation. This phenomenon is also applicable to other Bessel-like beams with nonlinear trajectories, which have been already reported.

We numerically demonstrate that the tight focusing of Bessel beams can generate focal fields with an ultra-long depth of focus (DOF). The ultra-long focal field can be controlled by appropriately regulating the order of the Bessel function and the polarization. An optical needle and an optical dark channel with nearly 100λ DOF are generated. The optical needle has a DOF of ∼104.9λ and a super-diffraction-limited focal spot with the size of 0.19λ2. The dark channel has a full-width at half-maximum of ∼0.346λ and a DOF of ∼103.8λ. Furthermore, the oscillating focal field with an ultra-long DOF can be also generated by merely changing the order of the input Bessel beam. Our results are expected to contribute to potential applications in optical tweezers, atom guidance and capture, and laser processing.

Monolayer group VI transition metal dichalcogenides (TMDs) have recently emerged as promising candidates for photonic and opto-valleytronic applications. The optoelectronic properties of these atomically-thin semiconducting crystals are strongly governed by the tightly bound electron-hole pairs such as excitons and trions (charged excitons). The anomalous spin and valley configurations at the conduction band edges in monolayer WS₂ give rise to even more fascinating valley many-body complexes. Here we find that the indirect Q valley in the first Brillouin zone of monolayer WS₂plays a critical role in the formation of a new excitonic state, which has not been well studied. By employing a high-quality h-BN encapsulated WS₂ field-effect transistor, we are able to switch the electron concentration within K-Q valleys at conduction band edges. Consequently, a distinct emission feature could be excited at the high electron doping region. Such feature has a competing population with the K valley trion, and experiences nonlinear power-law response and lifetime dynamics under doping. Our findings open up a new avenue for the study of valley many-body physics and quantum optics in semiconducting 2D materials, as well as provide a promising way of valley manipulation for next-generation entangled photonic devices.

偏振是光的固有属性之一，用于描述电矢量的振动方向，也是光场的一个重要信息参量。光场的偏振测量，尤其是具有复杂空间结构光场的偏振分布测量，是研究光场偏振特性及其应用的重要课题。本文从偏振测量的相关原理出发，总结评述近年来有关光场偏振分布测量和材料光学各向异性测量方法的发展动态，以及不同条件下光场的斯托克斯参量、光学各向异性材料的琼斯矩阵和双折射参数的测量方法及其应用。

Emerging as a family of waves, Janus waves are known to have “real” and “virtual” components under inversion of the propagation direction. Although tremendous interest has been evoked in vortex beams featuring spiral wavefronts, little research has been devoted to the vortex beam embedded Janus waves, i.e., Janus vortex beams. We propose a liquid crystal (LC) Pancharatnam–Berry (PB) phase element to demonstrate the realization of the Janus vortex beams and the modulation of the associated orbit angular momentum (OAM) and spin angular momentum (SAM). The generated Janus vortex beams show opposite OAM and SAM states at two distinct foci, revealing a spin-orbit interaction during propagation enabled by the LC PB phase element, which may play special roles in applications such as optical encryption and decryption. Other merits like reconfigurability and flexible switching between Janus vortex beams and autofocusing or autodefocusing vortex beams additionally increase the degree of freedom of manipulating vortex beams. This work provides a platform for tailoring complex structured light and may enrich the applications of vortex beams in classical and quantum optics.

Spin splitting of light originates from the interplay between the polarization and spatial degrees of freedom as a fundamental constituent of the emerging spin photonics, providing a prominent pathway for manipulating photon spin and developing exceptional photonic devices. However, previously relevant devices were mainly designed for routing monotonous spin splitting of light. Here, we realize an oscillatory spin splitting of light via metasurface with two channel Pancharatnam–Berry phases. For the incidence of a linearly polarized light, the concomitant phases arising from opposite spin states transition within pathways of the metasurface induce lateral spin splitting of light with alternately changed transport direction during beam guiding. We demonstrate the invariance of this phenomenon with an analogous gauge transformation. This work provides a new insight on steering the photon spin and is expected to explore a novel guiding mechanism of relativistic spinning particles, as well as applications of optical trapping and chirality sorting.

金属增材制造技术具有高效成型、节省材料和短加工周期等优点，能突破传统制造工艺的局限生产出空间结构复杂的构件，深受汽车工业、航空航天和医疗器械等领域的青睐。然而，增材制造技术在成形过程中产生的未熔合、裂纹和孔洞等缺陷限制了增材制造技术在工业上的推广与广泛应用。因此，金属增材制造产品的质量控制特别是在线监测具有重要意义。超声检测是材料内部缺陷最常用的手段。相较于传统超声无损检测技术，激光超声无损检测具有非接触、灵敏度高和适用于恶劣环境等优势，可以实现快速在线监测。本文扼要地介绍了金属增材制造和激光超声无损检测的技术特点，分析了激光超声的两种作用机制，简单地介绍了激光超声无损检测的原理和检测系统的搭建，系统地总结了国内外激光超声无损检测在普通金属材料和增材制造材料上的应用进展，并对激光超声无损检测技术应用于增材制造过程进行了展望。