2023, 50(18): 1813013
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.
2023, 11(9): 1553
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 DOF are generated. The optical needle has a DOF of and a super-diffraction-limited focal spot with the size of . The dark channel has a full-width at half-maximum of and a DOF of . 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.Bessel beam vector beam tight focusing depth of focus
Chinese Optics Letters
2023, 21(7): 072601
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.2D materials WS2 charged excitons trions indirect Q-valley valleytronics
2023, 6(4): 220034
Three-dimensional human pose estimation (3D HPE) has broad application prospects in the fields of trajectory prediction, posture tracking and action analysis. However, the frequent self-occlusions and the substantial depth ambiguity in two-dimensional (2D) representations hinder the further improvement of accuracy. In this paper, we propose a novel video-based human body geometric aware network to mitigate the above problems. Our network can implicitly be aware of the geometric constraints of the human body by capturing spatial and temporal context information from 2D skeleton data. Specifically, a novel skeleton attention (SA) mechanism is proposed to model geometric context dependencies among different body joints, thereby improving the spatial feature representation ability of the network. To enhance the temporal consistency, a novel multilayer perceptron (MLP)-Mixer based structure is exploited to comprehensively learn temporal context information from input sequences. We conduct experiments on publicly available challenging datasets to evaluate the proposed approach. The results outperform the previous best approach by 0.5 mm in the Human3.6m dataset. It also demonstrates significant improvements in HumanEva-I dataset.
2022, 18(5): 313
设计了一种基于先进外设接口(APB)总线的单线数字接口(OWI), APB总线可以配置接口参数并读取接口的状态、数据信息, 有着较强的灵活性与可监测性。该接口通过一根公用的数据线实现主机与一个或多个从器件之间的半双工双向通信。相比于其他通信接口, 线路简单, 节约了 I/O口资源, 降低了硬件成本。本文基于单线传输协议, 对数据传输时序以及状态机进行了设计, 通过寄存器转换级(RTL)仿真与可编程阵列逻辑(FPGA)验证, 结果显示数据可以稳定正确地通过单线接口进行传输, 数据传输速率可达 100 kHz。单线数字接口 APB总线 状态机 RTL设计 FPGA验证 RTL验证 OWI APB bus state machine RTL design FPGA verification RTL verification
2022, 20(10): 1046
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.Janus vortex beam liquid crystal Pancharatnam–Berry phase orbit angular momentum spin angular momentum
Advanced Photonics Nexus
2022, 1(2): 026003
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.
2022, 10(9): B7
2022, 49(14): 1402803